>Spirit dying is going to mean prices go up substantially across industry.

Maybe, but the economics of budget airline service are solid, so we will undoubtedly get new entrants. What wasn't solid was Spirit's outright disdain for their customers. It was completely unnacceptable how they operated, and the market has spoken as such. Even Frontier has humans you can talk to. Being stranded by one of Spirit's constant delayed flights with no recourse but an automated chatbot should have been illegal. It reached a point where your stated departure time was really no more than a vague suggestion of the time window you might be leaving around. They pushed the trend of service enshittification to its extreme conclusion and people finally had enough.