Viacom CEO Philippe Dauman’s relationship with controlling shareholder Sumner Redstone used to be so strong that few could imagine a change at the top.

But that’s quickly become topic No. 1 around the entertainment giant after Redstone fired Dauman and director George Abrams from his family trust and the board of his National Amusements theater chain — and appears to be planning to clean house at Viacom.

There’s no consensus, though, over who might take charge, and what that person could do to turn around the cable networks and movie studio owner which has lost nearly half its market value over the last two years as ratings and ad sales declined.

“If a leadership change is going to happen then investors may want to kick the tires on any new personalities before bidding up the stock,” RBC Capital Markets’ Steven Cahall says.

The most popular theory is that Redstone might want to recombine Viacom with CBS — a decade after he split the entities — and turn the enterprise over to the broadcaster’s chief, Les Moonves.

Those who like this idea say that this would simplify things for Redstone: He wouldn’t have to search for a new CEO and board for Viacom. Moonves is known and liked by the creative community, whose support Viacom needs.

With CBS and Showtime in the company’s collection of channels, there’d be less fear about cable and satellite companies dropping Viacom services including MTV, BET, Comedy Central and Nickelodeon. That’s been a concern since some small operators, including Suddenlink and Cable One, stopped carrying the channels and said it improved their profits.

Meanwhile, the opportunity to run Paramount would scratch Moonves’ itch to run a Hollywood studio.

“With each passing day and with each bizarre twist, we continue to believe that the mistake at Viacom happened 10 years ago,” MoffettNathanson Research’s Michael Nathanson says. “Nothing will be solved until the pieces are put back together again. We just aren’t sure how or when that happens.”

The concern is that Moonves is riding high now — CBS was the No. 1 network in primetime in the season that just ended — and might not want to take on Viacom’s problems. Some analysts say that there’s little anyone can do about the cable networks: The business may have peaked digital services including Netflix and YouTube become more competitive.

Cahall, for one, considers it a “relatively low probability” that CBS and Viacom would merge. “We do not think Viacom is an attractive asset to U.S. strategics as doubling-down on cable net exposure doesn’t make much sense given changes to the ecosystem,” he says.

If not Moonves — then whom? Here’s where everyone rounds up the usual suspects.

Tom Freston, the popular MTV pioneer who Redstone fired a decade ago, intrigues a lot of people. He’s friendly with Redstone’s daughter, Shari, who’s also President of National Amusements and Vice Chair of Viacom and CBS.

But it’s hard to imagine Sumner Redstone swallowing his pride enough to admit that he made a mistake. And Freston seems to be enjoying his work as a consultant to Vice Media and with his consulting and investing company Firefly3.

Wall Street would applaud if Redstone turned to former Disney COO Tom Staggs. After 20 years at the company, and one year as its No. 2 behind CEO Bob Iger, he startled everybody in April by announcing his plan to leave when the board declined to formally anoint him the heir apparent.

But Staggs has a long track record in finance, leaving some questioning whether he’d be the right person to lead a creative renaissance at Viacom.

DreamWorks Animation CEO Jeffrey Katzenberg’s name also comes up. He once tried to sell his studio to Viacom, and still had his eye on Paramount in early March when he told an investor gathering that his company could “bring a lot to that business.”

But that was before he agreed last month to sell DWA to Comcast. The companies expect that deal to close by the end of this year; it would be awkward for Katzenberg to leave before then to run a competitor. He also doesn’t have substantial experience in cable networks, Viacom’s core business.

Others on any list of possibilities include two of Rupert Murdoch’s former deputies at Fox: Peter Chernin and Chase Carey. Both are well known, and respected, managers with records of success in cable and Hollywood.

Yet Chernin seems to have his hands full at The Chernin Group, and working with AT&T at Otter Media. And while he and Carey are seasoned vets, that might send the wrong message if Viacom wants someone who’ll stay for years and excite the young audiences it needs.