On a state by state level, the fault lines would very likely resemble the old red state - blue state split, but even so, assuming states would hold in the event of such a scenario isn't necessarily realistic.
There are several states today that are pretty thoroughly divided, with a large urban area or two negating the political desires of the vast majority of the respective states in which they're located. Illinois, California, Washington and Pennsylvania are prime examples, with Virginia, North Carolina and Florida close behind, due to net in-migration of leftist voters from northeastern states.
Either there would be intrastate fighting to determine control or the state would split much as Virginia did over secession.
The will to fight and the cultural cohesion would go to red states and counties, but strategically speaking, the blue areas control the coasts and the ports even in the south. World opinion is now socialist opinion, so material support would likely be blue if proffered.
It would be a bloody, messy war with no clear favorite going in. Red would have to take certain blue areas to function economically. Ag commodities, oil and coal would largely lie in the red but it can't all exit through the gulf.
Tough call. Best to avoid it and part ways peacefully if at all possible.
I agree that would be the very best option.
Unfortunately, I don't think that's what's going to happen.