its what ATOL is for, insurance for exactly this sort of scenario. the airlines/tour operators pay for it and there's funding in place, even plane capacity on standby iirc, for it.
i may be mixing with another troubled business (though they often share the same issue), the banks/investors do apply rules, covenants, to the loans they make to the business. i.e. maintaining certain cash flow or margins. aircraft are a high capital investment they are leased otherwise a loan...
as i recall it from last year, their business is built on debt. the banks own everything so even though they announce a tidy profit they need to meet certain cash outflows and have bonds in place otherwise they cant fly.