It will be interesting to watch the core of what once had been America, self destruct. The sooner it happens the more likely that some recognizable essence of that will survive but I suspect that it will end up being unsalvageable. The change will be too extreme.
As to what will happen in the ‘heartland’, I think it is already apparent. Most of the people will leave for a variety of reasons but mostly because the climate will drive them out. The old and the hard bitten will stay until the last dog dies.
Most everyone else will move to cities and change. There will be a growing northern migration of those that want and need more space. That is, mostly, a different group. They will run into the problem of the Canadian border but that will be temporary. In thirty to forty years Canada will be a very new and interesting place.