I can't see the West Coast going to any trouble to hook up with the East Coast: they'd have their hands full trying to keep Southern California in the same country with Northern California, Oregon and Washington (who may find they have more in common with British Columbia than with anywhere else).
I also don't see the Mountain and Plains states submitting to the Southern or Gulf States. If you've already thrown off a government 2000 or so miles away, why bother with one 1000 or so miles away?
Even with all the political disagreements, states like Nebraska and Iowa or Colorado and Wyoming, even if they are on different sides of the red-blue divide, may still have more in common with each other than they have with states in another part of the country, even if they are on the same side.
It would certainly be ironic if the US split up, and then for the sake of survival different parts of the country -- the Mountain States or Middle West, say -- made the kind of compromises that would have saved the country if people had been able to make them earlier. But I can't see people creating some very complicated patchwork of borders to conform to political disputes elsewhere, rather than swallow a few disagreements in order to keep a state or a region together.
I can't see some massive Blue America Country giving up San Diego to some massive Red America Country, but maybe they could become independent Arizona's chief seaport. In any case, so much is going to change if something like this happens that any predictions made now are going to be proven mistaken pretty quickly.
“Assuming something like this happens, there would be more than one successor country.”
I think it would be very bloody in any case: I don’t see the libs giving up their workers utopia from sea to shining sea.
san diego or bust ...