No state possesses nukes, as far as I know. All nukes are on federal property and under the control of federal minions.
There would be some interesting legal details - like what to do about native american nations created by treaty; citizenship. I assume borders would remain open, trade would remain without duties, and so on. Might well be agreement to abide by some but not all federal edicts.
Just like Fort Sumter was in S.C.. 🙂