Ignoring bankruptcy for a second, big companies walk away from contracts all the time.  Those contracts normally stipulate that one company will pay another company a certain amount of money over a particular time period, which is effectively debt.<p>The difference between that and a mortgage is that the big companies are usually on a more equal negotiation footing than homeowners are with banks.  So rather than signing a boilerplate agreement, they have teams of lawyers to pick things over, write outs, etc.  So when they choose to "walk away", they usually have some reasonable way to do it and still comply with the contract.