Also, which discussion is referenced in question? Could you please give direct link?

@Ivan102f Referring to https://en.wikipedia.org/wiki/Dissolution_of_the_Soviet_Union

What if 1 state exit the union?

@Ivan102f Good question! My sense here is that the USA has not dissolved if there is still a globally recognized "government of the United States of America", so a single state seceding would be unlikely to cause that global shift.