With U.S. passenger traffic down by 90%, airlines are desperate to fill seats and are offering big incentives to keep their most reliable customers loyal. But what happens to frequent flyer miles when almost no one is flying and can an airline loyalty program survive if an airline goes bankrupt?

For the cash-strapped traveler who dreams of sipping champagne in first class, a frequent flyer program is a must-have.

Airline loyalty programs offer passengers free flights, seat upgrades and access