I would agree to the point of, JB needs to UP their offer, otherwise I see the SH's going with Frontier.Entirely different situation. AA was in bankruptcy and the unions at AA were on the unsecured creditors committee if I recall so they had veto rights over anything that was going to happen. Shareholders had no rights in bankruptcy.
Frankly, the way the market has been heading, Spirit's board is opening themselves up to shareholder suits if they don't give the JBLU bid a fair consideration. The value of the airline has dropped along with the market and the rise in fuel prices.
Taking it to a tender offer is indeed risky, but nobody holding an airline stock is getting a payday anytime soon. If JetBlue offers enough to entice 50%+1 shareholders to sell their shares to JBLU, it's game over.