An interesting part of nuclear strategy is that all meaningful countries are targeted, even though they aren't belligerents.

If the superpowers destroy each other, then whoever is left has the potential to become a regional power by virtue of not having been turned into glass.

So nuclear planning takes this into account. In other words, if the nukes start flying, then everywhere is fucked.

But WW3 doesn't necessarily mean nuclear Armageddon.