Brian Williams off the air. Will he ever be back?

Under fire for embellishing his reporting, NBC news anchor Brian Williams has taken himself off the air “for the next several days.”

"Upon my return, I will continue my career-long effort to be worthy of the trust of those who place their trust in us," Mr. Williams said in a memo to colleagues Saturday.

The question now is, will Williams ever be back in his capacity as the major voice and face of network news broadcasting? Speculation has begun about who might permanently replace Williams if it comes to that.

For now, his anchor spot will be filled by Lester Holt, who currently anchors ‘NBC Nightly News” on weekends and has filled in for Williams.

As is now well-known, Williams was not – as he claimed numerous times over the years – riding in a helicopter that came under enemy fire in Iraq in 2003. He’s apologized for that tall tale. Since that admission this past week, his recounting of events covering Hurricane Katrina in 2005 – seeing a body floating in the street from his hotel window in the New Orleans French Quarter – has been called into question as well.

Now, some of Williams’ other claims are being probed as well, going back to when he was a teenage volunteer firefighter, since then telling of the time when he rescued a puppy (or puppies) in a house fire.

The network, meanwhile, has begun an internal investigation of Williams’ reporting and assertions. It’s being led by Richard Esposito, the senior executive producer of NBC's investigative unit.

Can NBC credibly investigate itself? It’s a question many other top news organizations from the New York Times to Rolling Stone have had to face in recent years.

“In television news industry circles, there are many raised eyebrows about Esposito's assignment,” Brian Stelter writes at CNN Money. “But he is a well-respected reporter: he has a reputation as a ‘digger,’ someone who aggressively pursues subjects and scoops, not the sort of person who'd help make unpleasant news go away.”

Mr. Esposito’s digging may have to go deeper and wider than the known flap over the Iraq helicopter episode and Katrina.

“THIS was a bomb that had been ticking for a while,” columnist Maureen Dowd writes in the New York Times Sunday Review. “NBC executives were warned a year ago that Brian Williams was constantly inflating his biography. They were flummoxed over why the leading network anchor felt that he needed Hemingwayesque, bullets-whizzing-by flourishes to puff himself up, sometimes to the point where it was a joke in the news division.”

“But the caustic media big shots who once roamed the land were gone, and ‘there was no one around to pull his chain when he got too over-the-top,’ as one NBC News reporter put it,” Ms. Dowd writes, “It seemed pathological because Williams already had the premier job, so why engage in résumé inflation? And you don’t get those jobs because of your derring-do.”

Williams' importance to NBC News goes beyond his anchor status, Al Tompkins, a faculty member for broadcast and online at The Poynter Institute, a journalism think tank, told the Associated Press.

"He sets the tone of the network. It may not be as critical as when [Walter] Cronkite was CBS' anchor, in every way, but he is more than a face," he said.

Williams' absence itself is a delicate challenge, according to Tompkins.

"He can't be gone long,” he says. “The timing will be critical – too short and it won't seem like he has taken himself out of the game long enough, and too long and he looks like damaged goods."

Williams’ tarnished reputation – he’s become the butt of late night comedy TV and social media – obviously has rattled the network.

"It's shocking and profoundly upsetting," a former NBC News executive told the Los Angeles Times. "I'm not sure how he recovers."

Any further explanation from Williams himself could come Thursday when he’s scheduled to appear on the CBS “Late Show” with David Letterman – the same venue where in 2013 he retold the tale about coming under fire in Iraq.

“That is an incredible story … you are a true journalist and a war hero,” Letterman said at the time. “Incredible,” it turns out, was exactly the right adjective.