Nuclear war will never happen to be honest, and even if it does it's far from the end of the world.
The fact is that Nukes are simply a deterrent, if a countries got nukes then they're aren't going to be invaded, and even if they are invaded I still doubt the use of a nuke occurring, because the invaders don't want to ruin their prize and the people getting invaded would only massacre their own people.
In terms of terrorists using a nuke, or say for instance Islamic state, they won't use a nuke if they had one simply because if they used it they might get a few thousand people, but that opens excuses for everyone else to obliterate the Middle East, and permanent bury the threat for the rest of time.
So in short, nukes are there to make people feel safe, not to be used.