I'm pretty sure that when the advertised main event is cancelled, athletic commission rules state that refunds must be made available.
As for taking the event off PPV, that would just cost them even more money, because they'd have to pay out quite a bit to the PPV companies themselves, as well as satellite time buys, reimbursing event sponsors, etc. Better to take what buys come in, however few they may be. Moving to TV is 100% not an option.