My normally very forgiving mother took one set of flights on Spirit and refuses to ever consider flying them again due to their crappy "service." I tried to warn my parents beforehand, but they'd already purchased the tickets, expecting that any US airline would have at least some standards.

I don't think they have agreements with any other carriers to compensate for IROPS, so any foul up and pax are SOL.

Spirit has probably fulfilled the letter of the law by refunding the cost of the flights. I doubt Spirit will even consider anything more at this point. The only thing they might have considered was rebooking on Spirit on a later day, and probably should have been forced to do that. Award bookings and cheap ticket buckets on other airlines may have been grabbed ASAP by others stranded by this f'up, so I doubt there was any collusion by other carriers.