Which US Airline?
Coming back to Richard Branson's point, I would venture to suggest the answer might be that there will not be a "casualty" as such. Not that one, or may be more than one might become insolvent - but that the travesty that is "Chapter 11" will ensure that they a reincarnated - to fail again, and return to good 'ole chapter 11.
They certainly wouldn't be allowed to be taken over by any cash rich foreign investors (Emirates for example) - that would never do.