I think the scare stories of IRROPS are somewhat over blown. The ULCCs have about the same cancellation rates as every other airline and in some cases have actually bought their passengers tickets on other airlines. Spirit has significantly improved their operational reliability. Frontier has generally been pretty reliable after some rocky months after their purchase by Indigo. Allegiant I have no experience with.

In my case I take the chance and if necessary will book a walk up fare on another airline to get home, but I've never had to. I could probably book that replacement using credit card points of FF miles, but in any event I'm positive I'm so far ahead that I will still be ahead if it ever happens.