The short answer is nothing at least not in the short term. Now all the so called legacy carriers have been to bankruptcy protection and some even more than once. Continental Airlines, now part of United, went through this cycle twice in the 1990’s, and all the other legacies United, US Airways, Delta, and Northwest, now part of Delta, all went through this same process in the last decade. Some have suggested that AMR made a mistake of not going through this process when all of their competitors did.
During the chapter 11 bankruptcy protection it is easier for airlines to cancel leases and renegotiate other contracts. Quite a few of the other airlines dumped their pension liabilities to the Pension Benefit Guaranty Corporation during their restructuring.