I think before this all ends he's gonna start slinging tactical nukes* at Ukraine out of desperation/frustration.
* Tactical nukes aren't the city deleters, they're much smaller and meant to be used against military targets instead of entire regions. Their use wouldn't cause strategic level nukes to be launched in retaliation. Their use might cause NATO to immediately Wardec Russia though, but the threat of full strategic nuclear warfare might keep NATO from declaring total war.
I've learned to never say never, but if Russia uses even tac-nukes, the rest of the world will have no choice but to respond. This is how you lose China - who TBF isn't really doing anything, but "not being against us" is huge.
The reason is Ukraine is not an existential threat to Russia, just to their expansion plans. Having to use Nukes on Ukraine not only makes you look unstable, but worse than that it makes you look weak.
I do believe its possible Putin might give the order, but I doubt anyone with warhead access will obey.
Also remember that Russia's "Nuke Triad", in a conflict against NATO/US, is really a monoad. They don't have any advanced stealth strategic bombers. Back in the day, the operating ceilings of cold war bombers made them interceptor-resistant, but that was seriously degraded in the 80s and now is practically a non-factor. As a strike against NATO, their bombers are nearly a non-threat; they are still a threat for less militarily evolved neighbors though.
The US has B-2 spirit (and soon B-24 raiders) which is able to operate at high ceilings, with stealth, and incredible endurance. A B-2 Spirit could take off from Guam, and be going anywhere in the world. So if you are Russia, even if you suspect this a real mission targeting you and not the US fucking with you, you don't know where those bomebr will be coming at you from. They could even seem to be heading west, and the swing north and then strike St. Petersburg from the Barent sea.
Russia has boomers, but Russian boomers lack the stealth and operational capabilities that US subs have. An Ohio class can creep near the shore and launch submerged without support. Russian boomers need to have their surface navy pull security. Unlike the US where sub launches are a viable surprise first or immediate retaliatory strike from anywhere, Russian subs are ground-based launchers at sea.
(Also the US has enough nuclear attack subs they could task two subs to every Russian boomer, including the ones in drydock, and still have a few idle.)
Given the prevalence of US space imaging, and sub-fleet disparity, the "good enough" stealth and need to operate with surface navy security turns out to have not been that bad in the long term, and efforts that would have gone into trying to make them stealthy enough for independent blue-water operations were probably better spent somewhere else.