Using airline credits doesn't equal additional cash flow for the airlines. They already have the cash.
Not cash flow but they have to post it as a credit until it's used so it does not count as profit. So you will see a drain on cash but a profit for the airline.
The question will also be, what will they be charging? Airline travel had dropped down fairly cheap as of late. Last time this happened, they had to up their rates to clean things back up, so I guess that my credits will be worth 20-25 cents on the dollar when it comes time to use them.