I think Russian generals would mutiny before signing a death wish for their country by launching a nuke.
Either way, this war has already been a massive failure for russia. They were planning to take Kyiv in a week, annex some territory, and possibly install a puppet government before going back to business as usual.
If the war ended today with a Russian victory, it would be a pyrrhic victory for them. I feel like anything short of that will end with the overthrow of Putin. Their best chance of success is to keep meddling with the west in an attempt to sabotage Ukraine's support.