As cheap as fuel is they could still be profitable if they aren't burdened with too much in fixed type of expenses like pensions, facility rent, and plane leases or loan payments on their planes. If their labor is largely a variable component and airport costs are based mainly on arrivals and departures then those should survive. No telling what the pilots, flight attendants, and mechanics unions could be demanding though. Or if agreements with airports are long or short term with flexibility related to volumes. And if they have too many planes parked and out of service.