Does anyone really think that NATO will risk a nuclear holocaust if Russia were

[Justice matters.]

72. Absolutely NATO would respond because...

first, it starts with 1, 2, or 3 countries under attack, then another, then another (or not).

The point being, once we don't respond to a commitment by treaty (serious stuff), nobody really knows what the illegal invaders will do next after seeing our weakness in not following up as we signed we would.

As for Russian military using nuclear devices on any NATO country, that would be the craziest SUICIDAL thing they'd have ever done:

How likely is the use of nuclear weapons by Russia?

Exploring key questions around Putin issuing what was interpreted as a threat to use nuclear weapons against NATO countries if they interfere in Ukraine.

https://www.chathamhouse.org/2022/03/how-likely-use-nuclear-weapons-russia

It's a bluff, IMHO. they do have "silent" submarines not far from our shores also, but we also have some sailing not far from theirs.