Imagining Citicorp after Charles Prince or Bear Stearns after James Cayne has long been a popular game on Wall Street. The calculations about what happens next at Merrill Lynch after Stan O'Neal have had to ramp up almost overnight.

The rapid and spectacular fall of O'Neal is expected to become official soon. Reports say that O'Neal has agreed to resign and is negotiating the terms of his departure. That will mean a payday of at least $159 million if he steps down, according to an analysis done for the New York Times, but less than if he left as a result of a merger.

The exit of O'Neal, the New York Times says, underscores that "on Wall Street, even the highest-paid chief executives with handpicked boards are not immune to the furies of investors and employees."

And those are the two constituencies that the new chief executive will have to mollify in the beginning.

The next C.E.O. will have to restore investor confidence that was damaged by the size of the third quarter write-down ($8.4 billion) and by the way it was disclosed (with a warning and an upward revision). A Wall Street firm is only as good as its reputation, and Merrill's is in need of repair.

The new chief will also have to act to prevent internal bitterness over O'Neal's five-year tenure from erupting further. O'Neal transformed the traditional culture of "Mother Merrill" and made it a leaner, less-risk-averse firm. While those changes created a lot of ill will, there is no going back to the old ways of doing business.

The front-runner for the top job is, by all accounts, Laurence Fink, the chief executive of BlackRock. The investment management firm has been a bright spot for Merrill since it took a nearly 50 percent stake in it last year. One of the most admired executives on Wall Street and one with a reputation for strong risk management, Fink has often been cited with possible top jobs on Wall Street.

An architect of the BlackRock deal, Greg Fleming, is another leading candidate. But he also was involved in O'Neal's ill-fated overture to Wachovia, according to the Times, and that could hurt his chances.

Another internal candidate is Robert McCann. He heads the 16,610-strong brokerage division. Until recent years, that had been the engine of growth at Merrill and the business that served as the stepping-stone to the C.E.O. suite.

The Times reports that the board is also considering promoting McCann to co-president with Fleming.

Then there is John Thain, once a strong candidate for the top job at Goldman Sachs. Thain is president of the New York Stock Exchange, but having navigated the exchange through mergers with Archipelago and EuroNext, and through its transition to a publicly held, increasingly electronic marketplace, he may be ready for a new challenge.

And if every Wall Street firm wants to be like Goldman, the Wall Street Journal reports that two current Goldman executives, Gary Cohn and Jon Winkelried, "could be wild cards in the race."

Other names that have been thrown about include Alan Schwartz, president of Bear Stearns, and Robert Diamond, president of Barclays.