the problem with relying on "mutually assured destruction" is that it requires presupposing rational actors on all sides. But when an oligarch starts to accept that their adventurous life of debauchery, decadence, violence, and obscenity in all three realms is no longer going to continue, i don't think they even CARE about how anyone else feels or whatever happens after they're gone.
so, yeah, i think they WOULD in fact nuke europe. Possibly even chuck 'em at every NATO nation because they keep beating the dead horse of claiming that ukraine is being puppeted by NATO.
It would be nice if it turned out that whoever is sitting in the missile silo command centers has better morals than the scum fleshwastes who are in charge, evading armageddon via conscientious objection AGAIN just like that one time a radar malfunction over the northern arctic almost caused russia to preemptive strike the united states back during the cold war but for ONE DUDE who decided he wouldn't make the call that could end the world.
it's lowkey akin to a narcissist's 'extinction burst'. they're losing everything so they blow up and burn it all, shrieking incoherently from their quivering ball of white hot impotent rage "YoU mAdE mE dO tHiS!1!!!11one!1!1!1"
EDIT:
BUT FOR REAL, ALL THAT SAID, I don't even really disagree with you THAT much. Because if it IS a rational actor, they probably WOULD decide as you predict...
... IF a rational actor x.x