Bank of America

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CEO Ken Lewis' decision to buy

Merrill Lynch

has come to look like a big mistake over the past several weeks, but speculation about his departure may be premature.

The resignation of former Merrill CEO

John Thain

from BofA Thursday has highlighted the unforeseen difficulties in merging the two firms, meaning Lewis is facing additional heat. NAB analyst Nancy Bush said in a

Wall Street Journal

report she believes Lewis could be "gone next week."

BofA dismissed Bush's prediction, but Merrill's staggering $15.31 billion fourth-quarter loss has caused many to question Lewis' judgment in signing on to the deal. The Treasury Department's investment of an additional $20 billion in bailout funds and $118 billion in loss protection against Merrill's assets has further spurred the belief that Lewis' Merrill purchase was a bad buy.

However, not everyone believes Lewis is headed for the exits.

"I don't think there's any chance that Ken Lewis steps down without this company being in a position where the outlook is much improved," says Anthony Polini, a Raymond James analyst who covers BofA.

He said that pending a turnaround for both the company and the industry at large, Lewis will keep his post. "The last thing you're going to see is Ken Lewis leaving this company with heightened investor concern or risk," Polini says.

Richard Staite, U.S. banking analyst for Atlantic Equities, agrees. "He's clearly under pressure, but I'm not convinced that he will resign," he says. "Simply getting rid of the senior management isn't necessarily the answer to all the problems there."

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Staite says the banks generally need stability as they attempt to negotiate deteriorating loan portfolios, and that questions of management succession are secondary. That said, "It's clear the

Merrill integration is not going well," Staite says. "That's very clear. The two sides need to work on smoothing over their differences."

Even if a near-term departure by Lewis would come as a surprise to some, the question remains whether Thain's departure has disrupted BofA's line of succession when the 60-year-old CEO does leave, via retirement or otherwise. Brian Moynihan, BofA's general counsel, on Thursday was named to replace Thain as BofA's president of Global Banking and Global Wealth and Investment Management. He appears to be a strong contender to succeed Lewis, Polini says.

"Whether or not Thain could've provided additional competition, we'll never know," he says.

Some had speculated that Thain, who earlier in his career served as CFO of

Goldman Sachs

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and CEO of

NYSE Euronext


, could be eyeing BofA's top job when Lewis moved on. Polini says that Thain's resignation may have even removed uncertainty about the future of the company. "Maybe actually

the company is back more on a normal track," he says. "Thain ... was more of a variable."

On a symbolic level, however, Thain's departure has hurt the integration between the two firms, says KBW analyst Jefferson Harralson. Although it might have been worse to lose Merrill's brokerage-unit head Bob McCann, "Integrations are very sensitive already, and losing your integration leader is a hurdle."

CEOs are often judged by the success of their big deals, but a judgment of the Merrill deal a mere 22 days after its closing would be premature, says Harralson. "I suspect Ken Lewis will be given time to see if the deal works," he says.

Whatever may become of Lewis and the rest of BofA's management team, the road ahead is difficult. Bank assets continue their broad decline, unemployment continues to rise and the housing market continues to spiral.

"There are no magic solutions to the problems any of the banks have got," says Staite.