The Soviets would probably the ones starting the use of nuclear weapons, which was visible in their exercises and plans.
it was visible in both. both knew they would be used as each side had them. the question is at what level. tactical battlefield or city busters launch them or loose them. once you start using them on the battlefield no one is going to think either side is going to refrain from the rest. so the matter goes from fools errand to a very bleak week for mankind.
scenario 1. Soviets look to be winning, the british and French and US forces will launch..
if it looks like the west is going to win and there can be no negotiated hey .. oops .. our bad type peace, then the Soviets are going to launch.
let's say it stays conventional just for giggles. the Soviets make it to Frankfurt while the west is building up and throwing everything into a defensive line from Denmark to the alps.
this line is going to buckle a little. the second West Germany falls things are going to get ugly very quick. do we refrain from bombing enemy cities and factories with conventional ordinance? what do the soviets do when a mass of bombers cross the border, how do you know what is in the bomb bay?
do the soviets attempt to strike US soil with bombers and conventional bombs? how does the US know what is coming.
This is reason number 1 why the two sides never went head to head. no one could or can know. the closest they got was cuba and that was about 40 seconds from being very stupid. both sides while not friends, are in no way looking to sacrifice themselves.
So as I said earlier, This would be an all in act of desperation by the soviets. The whim of a General staff that has gone off the deep end.
I also have to question the Loyalty of non-ussr eastern block states, as I think the whole house of cards would come down if such a thing was attempted in reality. the memories of WWII are still quite fresh and now for a third time in 60 years Europe is in flames and this time bound to glow in the dark.
Cuba was the last time that East West was going to nuke each other into oblivion on purpose, and they chickened out there since well.. Moscow for Havana or DC for what?! the logic doesn't exist to support it.