It is indeed Ironic that a nuclear confrontation would invariably and specifically devastate the leftist population, leaving the bulk of the rural and suburban conservative population more or less intact. Indeed generally speaking most people would be surprises just how much of our population would in fact survive a real nuclear war. And your not even talking abut something even approaching that in the even of a Civil War. Nether side has a vested interest in destroying the other, least of all the side that wishes to rule the other.
The objective of the revolutary would have to be a MAD policy at least long enough to secure their independence. The objective of the imperial government would have to be to recover control of their weapons and disarm the breakaway republic so that it can be conquered.
Frankly the revolutary state might even agree to give them back to nukes in exchange for recondition of their Independence and a resumption of peaceful trade relations.
While we may not trust the leftist with direct power over us as to vote away our rights, we probably would trust them to respect our borders, at least long enough for us to firmly establish and entrench our own defenses & relations with the world.