Naively, UK disarmament in 1980 would have done one of two things 1) given the Soviets under Brezhnev much more power, lengthening the cold war and producing unknown effects on reform; or 2) forced even more US nuclear deployment in European bases, forcing a response from the Soviets, and so destabilising the world. (As I say, there’s a chance that it could instead have lead to a better equilibrium, but I can’t see why anyone would think this was the most likely outcome.)
If the locations of your post-nuke decentralised government are known, then they can be targeted by nukes.
Naively, UK disarmament in 1980 would have done one of two things 1) given the Soviets under Brezhnev much more power, lengthening the cold war and producing unknown effects on reform; or 2) forced even more US nuclear deployment in European bases, forcing a response from the Soviets, and so destabilising the world. (As I say, there’s a chance that it could instead have lead to a better equilibrium, but I can’t see why anyone would think this was the most likely outcome.)
If the locations of your post-nuke decentralised government are known, then they can be targeted by nukes.