Not really. It was only decided for that particular instance. And the winning side had to bypass the Constitution in many ways to get it done. (Read one of the many books on how Lincoln acted in many non-Constitutional ways.) The issue of secession is not settled in the least. And who is to say who would have the biggest army this time?
That's what I said ... in the absence of a political agreement amongst all the states - such as when Czechoslovakia separated - then force of arms will decide.
We know how that worked in 1861-65; we don't know how it would play out a second time.