Indeed. It's the whole reason to never allow a nuclear conflict to erupt in the first place. And particularly to not get into a scenario where a weak third world type power can threaten the existence of a superpower (because it may topple the MAD premise in the after-consequences; MAD has a rarely discussed psychological requirement involving the people of a nation: acceptable parity exchange, aka great powers with a lot to lose choosing to not destroy each other; ie how does a superpower react to being destroyed by a country like NK? what's left of MAD afterward?).