Bankruptcy is certainly possible, but those are something of a fact of life for the airline industry.

i think the major airlines all exist under the "too big to fail" umbrella, and will be bailed out by the goverment in some fashion before they actually collapse.

however, as long as they can cut expenses by laying off staff with no consequences, they're probably safe. previous tough times for airlines haven't been in quite the same situation where they can just cut expenses by cutting flights. i'd be more worried about the airports than the airlines - at some point, they're going to have a big backlog of fixed non-staff expenses that are no longer being covered by ramp fees.

We're not that lucky.

IIRC American has some serious debt issues but Delta and United are sufficiently solvent that they'd get bailed out.

Nope. See also: Amtrak.

On the contrary, Amtrak represents the exact scenario that OP was asking about. It was created following the complete collapse of all the major passenger railroads.

I think the point was "there'll always be passenger service", not "the current companies will survive unscathed".

The worst case is they could all merge into "Amwings" and those who choose to AGTOW would go bankrupt. I doubt it. Consolidation down to fewer major carriers per country would happen first because it's not like HYPErloop is going to put airlines or air cargo out of biz anytime soon.