Edit: WHAT I WROTE BELOW IS WRONG BUT I'LL LEAVE IT THERE SO YOU CAN READ HOW I WAS WRONG

Just wanted to note that anytime I need to get back from a Spirit RT, I've been purchasing AIG Travel Guard silver. It is really really cheap (between $15 and $20 per trip) and provides 100% of the declared non-refundables, but also provides $500 in trip interruption coverage. Basically, if spirit cancels the return then it pays up to $500 for any other flight (minus whatever Spirit refunds you). (EDIT: ONLY FOR 24 HOUR WEATHER DELAYS)

Cheap cheap peace of mind if you absolutely have to get back.

*Note, I'm 30 and part of the coverage has medical coverage, so for my 75 year old stepdad it was significantly more.