"I think it's inevitable that Les is history at CBS, whether he takes a leave of absence or is dismissed outright," Bibb said on CNBC's "Power Lunch" Monday, ahead of the CBS board's decision to seek outside counsel to investigate the allegations against Moonves.
The board, which made no decision about Moonves' role at the company, also said Monday afternoon that it's postponing its annual shareholder meeting, which had been scheduled for Aug. 10.
Bibb, managing partner of corporate finance at Mediatech Capital Partners, said Moonves' own statement regarding The New Yorker report on Friday could be "the final blow."
In a statement, Moonves, who has been the CEO of the network for more than two decades and chairman of the board since 2003, said, "I recognize that there were times decades ago when I may have made some women uncomfortable by making advances. Those were mistakes, and I regret them immensely. But I always understood and respected — and abided by the principle — that 'no' means 'no,' and I have never misused my position to harm or hinder anyone's career."
The New Yorker's article published Friday looked at the corporate culture at CBS and allegations of sexual misconduct against Moonves between the 1980s and 2000s.
Shares of CBS closed down another 5 percent Monday, on top of the 6 percent they lost Friday.
Meanwhile, Wall Street analyst Tuna Amobi downgraded the stock to hold.
"There's usually a cloud that kind of lingers when you get this type of announcement," Amobi, who works at investment research firm CFRA, said Monday in a separate "Power Lunch" interview.
"If you look back, the stock hasn't really done much the last couple of years," he said. "There's no questions that Les Moonves has a stellar track record. But having covered this stock, there's always this kind of disconnect between the fundamentals and the recent price action."
Amobi said he shares the view that Moonves is unlikely to last as CEO of the company following the allegations. But he added the odds of a CBS-Viacom merger have been "enhanced by this situation."
"Redstone is very likely to have her wish and be able to combine Viacom and CBS and then sell the combined companies," Bibb said.
CBS and Viacom were under the same umbrella from 2000 to 2006 before they were split into separate publicly traded companies.
CBS could not immediately be reached for comment.