end of the world shit if you live in the west.
How do you figure that??? Most of the west is actually farming and ranching country. We get along well without the city folks. We are well armed and well prepared to take care of ourselves. It sounds like you think the west is all LA and SF.
No power, no water.
lots of reasons - people living in the country for the most part aren’t already organized to deal with large-scale incursions. also, if it is bad enough, the military may present a problem if they decide to take possession of suspected stockpiles or other facilities. The army is going to eat, no matter what anyone else does.
some geographic areas might do fine, but the country as a whole, both geographically and population-wise, wouldn’t.