Let’s just say the firing of AOL CEO Randy Falco and President Ron Grant was not exactly expected–even if everyone thought it should happen–within the high ranks of the troubled online unit, until Time Warner (TWX) CEO Jeff Bewkes dropped the guillotine this afternoon in Manhattan.

And drop it he did, quickly lopping off the pair of executives Bewkes had installed himself. He replaced them with Tim Armstrong, Google’s head of advertising sales, a man with a much brighter resume, for what is likely to be an attempt to spin out AOL now that merger options are moribund.

“It’s a shock to everyone how sudden it was,” said one exec. “Everyone talked about when Bewkes was going to run out of patience with Randy and Ron all the time, but no one knew it was coming now, since it had taken so long.”

Grant, for example, only found out about the situation when Bewkes told him in person earlier today at AOL’s offices in lower Manhattan, said several sources. Bewkes has hardly ever been there–he has a stunning office at the Time Warner Center in midtown–although Armstrong’s office at Google is nearby.

Falco might have learned about the situation earlier, but several sources said no other top exec at AOL did until about 30 minutes ago.

The whole coup came, said several sources, from corporate, which swooped and made the moves swiftly, very quickly after signing the deal with Armstrong.

(Here is an interview I did this afternoon with Armstrong after the appointment was announced.)

AOL PR did not seem to be aware of the move until this afternoon, and neither did its three top division heads: People Networks head Joanna Shields, MediaGlow President Bill Wilson or newly hired Platform-A ad leader Greg Coleman.

Yesterday, quite by coincidence, BoomTown wrote about the continued turmoil within AOL and the unhappiness with Falco, which was long-running:

“That’s caused a lot of people inside AOL and also a wider circle at Time Warner to increasingly point the finger of blame at AOL CEO Randy Falco, wondering if and when he will suffer too.

“‘Why Randy Falco gets to keep his job is a mystery to a lot of people,’ said one top exec at another division.”

Well, it is a mystery no longer, apparently, with Bewkes putting the high-profile Armstrong in place as AOL’s CEO and chairman, although he has been casting about for new leadership for a while, according to many sources, such as former Yahoo COO Dan Rosensweig.

AOL is in the midst of laying off 10 percent of its staff of 7,000, although many feel deeper cuts are needed, especially since Bewkes has been unable to complete a deal to sell it after a lot of trying.

Interest by Yahoo (YHOO) in merging with AOL, for example, has cooled and there seem to be no true suitors on the horizon. A spinoff of the division seems to be the most likely option.

Whether that includes a strategy reset for AOL or not is unclear.

Under Falco and Grant–who were derisively given the nickname Smithers and Burns from “The Simpsons,” and also “Rondy” by some inside the division who did not like them–AOL paid $850 million for the Bebo social-networking site last year, an overpriced move that has grated on many throughout Time Warner.

Under their plan, AOL was focusing on a three-pronged strategy: social networking and communications (People Networks), content (MediaGlow) and advertising (Platform-A).

But new Platform-A head (and former Yahoo sales exec) Coleman–whose business has to drive revenue growth–cannot perform miracles in such a weak environment no matter what cool new products and offerings either People Networks head Shields or MediaGlow president Wilson create.

Armstrong certainly knows sales, as head of sales efforts at Google (GOOG), although he has never operated a business as multi-faceted as AOL, which–despite its troubles–remains huge.

More to come soon…

And, no surprise, he is the No. 1 choice of most inside and outside Yahoo (YHOO) in the wake of the news late yesterday that current CEO and Co-Founder Jerry Yang is stepping down.

And why not? Chernin has the right resume: Experienced at running large and complex organizations; savvier than most in media about the Internet; able to make the kinds of dramatic decisions needed; and, perhaps best of all, signaling–via the Los Angeles Times–just this past week that he was open to leaving the powerful media and entertainment conglomerate for something new.

Well, Yahoo would certainly be new for Chernin, in terms of a corporate cleanup challenge, especially compared to figuring out how to make bank on plush toys from “The Simpsons.”

And, while the risks are many, if Chernin (pictured here) managed to turn around Yahoo, he could make a huge fortune too, given Yahoo shares have languished of late, much in the same way they did when former CEO Terry Semel came to Yahoo from Hollywood in 2001.

But it’s not altogether clear whether Chernin would actually leave his powerful perch at News Corp. (NWS)–which owns Dow Jones and owns this Web site. He has been ensconced there for a dozen years, building a huge reputation as a sharp exec (No, Peter, I am not kissing up, as I think Yahoo would wear even you down very, very quickly).

That’s even though many note he is not likely to take over as CEO from its iconic leader, Rupert Murdoch. The media mogul is widely expected to favor one of his own children to lead News Corp. next.

And the 57-year-old Chernin already makes close to $30 million in his current job, which is definitely challenging.

And, although Chernin has been involved in the News Corp.-owned MySpace and has had success backing the Hulu online video site, it is not nearly as hard as the five-year turnaround quagmire (plus no fabulous media mogul perks either) that Yahoo could turn out to be.

In addition, privately to other News Corp. execs, Chernin has regularly pooh-poohed a move to a digital company, even though he is always on the short list for a lot of big Internet jobs–such as the long-unfilled post as digital head at Microsoft (MSFT) more recently.

So, who else to take over from Yang, who will return to his job as Chief Yahoo after stepping down from the company as soon a search for a replacement CEO is successful?

Well, here is BoomTown’s own shortish list, based on asking a wide range of people inside and outside Yahoo, all of whom are important digital players in their own right.

INSIDE YAHOO

Sue Decker:

The current President of Yahoo is certainly being “considered” for the job, which is a polite term for not really being considered at all. While Decker is an intelligent and thoughtful exec, like a politician with a record, she has had her hand on the operating tiller at Yahoo for too long not to get deservedly blamed for its current situation.

In addition, she is radioactive to big investors, who have told the Yahoo board in no uncertain terms that she is a nonstarter.

Maggie Wilderotter:

The former Microsoft exec, who has also been a public company CEO, is an interesting idea floated by some, who think the Yahoo board might turn to one of its own directors, as a short-term solution to stabilize Yahoo.

Wilderotter has been much focused, said several Yahoo execs, on cost-cutting at Yahoo and certainly is not as tarnished, being a more current board member. But she is a largely unknown quantity in the Internet space and, most importantly, at Yahoo.

John Chapple:

The former CEO of Nextel is one of the two board members (former media Frank Biondi Jr. is the other) recently picked by Carl Icahn, when the activist shareholder was admitted on the board as part of the proxy fight settlement.

Chapple has, sources said, been conducting chats with Yahoo execs lately, perhaps as a way to get a lay of the land. If he got the job, it would be clear Icahn had won his Pyrrhic victory (and personal financial defeat) against Yang.

OUTSIDE YAHOO

Dan Rosensweig:

The very funny, but brash, former Yahoo COO is definitely a favorite within Yahoo’s ranks, except for those who don’t like him. But it’s clear Rosensweig does know and love Yahoo, is close to Yang and, ironically, enjoys a tight relationship with Microsoft CEO Steve Ballmer, who also wanted him for the digital head job.

Also, Rosensweig, who does have operating chops, has gotten some much needed time away from Yahoo, as a partner at the tony media investment firm, the Quadrangle Group.

Meg Whitman:

Another dreamy CEO choice, except she has already been a big company CEO at eBay (EBAY), has proved her mettle in building it to a powerhouse–despite the online auction site’s currently harder times–and has the giant fortune to prove it.

And, oh yes, she is likely to be using that pile of cash to run for governor of California, on the Republican ticket.

Jon Miller/Ross Levinsohn:

The Bobbsey Twins of the Internet, the pair are now having a very good time running their own investment company, the Velocity Group.

But, aside from some questioning whether he can make the quick decisions needed at Yahoo, Miller (pictured here on the right), the former head of AOL, does not want to leave his New York home and cannot take any job anyway until his noncompete with Time Warner (TWX) runs out in March.

And former Fox Interactive Media head Levinsohn likes Los Angeles, and probably is too fast a personality for Yahoo (his going there would be a shock to its system, but would be endlessly entertaining to me personally).

Tim Armstrong:

The top ad exec at Google (GOOG) certainly is an interesting idea, although has little of the product experience needed to run Yahoo. But he is a well-respected advertising figure–where Yahoo needs to shine–and could do well with a lot of strong execs under him.

He is also not on a CEO path at Google–paging, Larry Page!–and could be interested in proving he could run a company on his own.

Kevin Johnson:

The former Microsoft exec was supposed to be running Yahoo, if he and Ballmer pulled off their takeover attempt earlier this year. They did not, and Johnson then left Microsoft to run Juniper Networks (JNPR) in Silicon Valley, right up the road from Yahoo, in fact.

But Johnson is likely subject to a noncompete by Microsoft and a strong contract at Juniper too. Still, a very sharp exec, he definitely has the operating, political, technological and digital skills to take on Yahoo. Also, ironically, he and Yang really get along well and like each other, despite the takeover battle.

Of course, there are a lot of other ideas: Disney (DIS) online exec Steve Wadsworth; the outside-the-box choice of former Procter & Gamble (PG) marketing wizard Jim Stengel; Microsoft digital exec Yusuf Mehdi; CBS (CBS) digital head Quincy Smith (whose hyperactive dealmaking would likely lead to a mutant merger between CBS and Yahoo); and former Cisco (CSCO) and current Joost CEO Mike Volpi.

Please post suggestions below or, better yet, send tips to me at here.

Please see this disclosure related to me and Google.

The motto: “I, for one, welcome our new AOL overlords.”

Why shouldn’t they? As BoomTown reported, every Bebo employee has had their previously granted stock options accelerated and fully vested under terms of the deal.

This is typical in acquisitions by the Time Warner (TWX) online subsidiary, since it cannot offer enough of its moribund old media stock.

Unfortunately, those kind of deal terms don’t make for the kind of environment that encourages already jumpy entrepreneurs to stay. In fact, it kind of gives them a free pass to leave.

Still, it is nice to see Bebo minions celebrating their new bosses, including AOL CEO Randy Falco and President Ron Grant, who helmed the Bebo deal.

But to clarify for Bebo staff: Falco and Grant’s nickname at AOL is Smithers and Burns, that lovable pair from “The Simpsons,” and not overlords.

It goes without saying that further errors like this will not be tolerated.