Another mainline airline buying Frontier in its current state means the buyer might get forced into taking a bunch of RJ pilots who are not trained on any equipment the buyer operates, and some of the RJ pilots may feel entitled to get integrated into the buyer's seniority list able to hold Captain! For another mainline carrier to buy Frontier would be an instant way to start a war with the current pilots - an expensive war.

The impediment to shedding Frontier for Bedford isn't in his own company (those costs are going to have to be dealt with on his balance sheet as part of buying Frontier), its trying to sell such a toxic asset to another company.

What assets does Frontier have that could make inheriting a seniority mess worth it? Does RAH have any LGA or DCA slots that could be thrown in to sweeten the deal?