Doubtful. People will either just eat the higher costs or simply drive. The infrastructure is lacking (relative to airports), and there's unlikely to be any support for expanding it anytime soon - passing costs on to consumers is the current US culture.
Those airplanes aren't going to be scrapped. Demand for flights hasn't reduced much. Other airlines will buy up the airplanes and put them back into service.
Really? Spirit had a very limited route network. And Delta and United have been successfully pursuing a market strategy based more on service quality than low prices. They account for the majority of profit in the whole industry.
My point/question is whether this will reduce air travel and increase demand for rail.