I'd be very very surprised if OATS went bust with the assets of its parent company BBA Aviation plc behind it, unless said parent company went bust, which is unlikely IMHO.
There might be an orderly retreat from commercial training, though, but I'd expect that in that scenario refunds would take place, or students would be allowed to finish their courses.
That's not to say that some smaller schools without strong backers might not go bust though - demonstrably over the last few years they can and have.
cheers!
foggy.