For Citigroup and its embattled leader, Vikram S. Pandit, the terrible ifs are accumulating. Word that Mr. Pandit would try to salvage his troubled bank by cleaving it in two was greeted Wednesday with stunned disbelief on Wall Street. Rather than calming skittish investors, the plan stoked fears that Citigroup — and indeed the broader financial industry — was entering a perilous new phase in the financial crisis. Mr. Pandit wants to sell a range of unprofitable businesses and troublesome assets, including some with roots in subprime lending. But investors wonder whether other financial companies will have the will or the means to buy them. Like Citigroup, other banks need more money to withstand yet another looming wave of red ink. Bank of America was negotiating on Wednesday for a second multibillion-dollar round of federal aid.