Gotta tell ya, the Arm Chair CEO's are truly an interesting group. (Don't take offense - I count myself among them)
BB recognizes that as a Regional he is going to make his money a few years at a time with an overall but "ever-slightly-adjusted" long term strategy. Consider the possibilites -- BB guarantees to loan $25M. He settles the $260M claim for actual lost income and expenses -- lets say $10M. Lynx ends up the fourth leg of Republic, which BB gets for pennies on the dollar. (Worst Case) Republic flies the Frontier routes for 3 to 5 years making money all along the way and bang Frontier does not make it. BB ends up with the gates to either market to another code share or sell to SW. Almost no matter how you think this plays out -- BB and Republic win. All for an up-front expense of maybe $15M. One plane costs him more than that.
FYI - SW does not even want most of the routes Frontier has. Secondly, Southwest absolutely wants to keep Frontier alive, but weak. Denver is a great market and the last thing SW would want is a threat from a strong competitor entering upon Frontier's exit. (Let's see -- who could help make that happen). SW is not going to kill them, they will probably supply the defibrilator to keep them alive.
The good Reverend took some short term pain for long term gain by agreeing to gracefully bow out last April. Count on it, he has a plan and is going profit big from this deal.