I think it's hard to say what would happen if a major airline shutdown since it's been so long since it happened last. Pan Am and Eastern's programs were taken over by Delta and Continental respectively in 1991. TWA's was taken over by AA in 2001, but that was more of a merger.

In theory a bankruptcy court could invalidate the FF program, but it's never happened in any of the numerous reorganizations because it would be too disruptive to the business.

The minor programs have been left out to dry -- ATA Travel Awards, Aloha AlohaPass, and Independence iClub are all worthless.