I would think some routes will work in the long term - especially those in Florida and (to my surprise) RDU, while I think Columbus will soon go away, probably before Cincinnati service starts.

However, if you are getting 80%+ load factors, even with reduced fares, they should make some money. Don't forget all the luggages fees you have to throw in to the mix.

Besides, where else would Frontier get such a long term deal on landing fees?