If so, now we're positing a dying insane man who is willing to use nukes because he fucking feels like it.
Which means the west has absolutly no choice but to remove Putin and the ruling regime because you can't reason or negioatie with someone like that. We'd have an obligation to basically disarm Russia like we did Germany and Japan to keep such a thing from ever happening again.
And yes, the thought is terrifying. MAD assumes sane rational actors in charge of nukes who won't use them for fear of being completely annilated. Putin deciding he's willing to burn everything to ground invalidates this. The problem is, letting him deploy nukes without consequence is possibly worse, because it also invalidates MAD and it just encourages more use of nukes as a form of extorsion. If Russia can use a nuke and the west doesn't immediately respond with consequences,(like the destruction of the Black Sea fleet for starters) there's no reason to think he won't do it again in Eastern Europe(like, say, Poland). Or China invading Taiwan and using Nukes because they know there are no consequences for doing so.
A person going insane isn't a problem. No autocrat functions alone. The problem is that he has a population that vastly supports him. And that population isn't made of aliens. That population is made of us. Of the humans defined and overcome by hardcoded assholery, as we see throughout the world again, with Republican in the USA, with Talibans in Afghanistan, with Erdogan in Turkey, with Mitsotakis in Greece, with Museveni in Uganda, with all these copy-pasted dipshits all around the planet, driven by the same mechanisms. It's mankind.
Fearing the planet to nuke itself (to nuke itself instantly, as opposed to roasting itself fast for short term complacency, profit, comfort, vanity and stupidity) is fearing a deviant minority of humans to pay the price for what the species is as a whole. But it happens, fast or faster. You can wish for some lucky decent people to be roughly spared for a few more moments, but the equal proportion of decent people will run out of the same luck, run out of the same time, as mankind as a whole, eventually. Making it futile.
Putin is a negligible symptom. His fans, and the fans of his morally equivalents worldwide, are the reality.