What would even be the consequences if Russia were to use nuclear weapons in Ukraine? Maybe a lot, or maybe absolutely none depending how they are used. If they are used in a Nagasaki capacity then yeah, that would lead to repercussions, but you can do that with conventional arms too. See what the allies did to Dresden for instance, or the firebombing of Tokyo. The issue is not the weaponry, but the act of threatening civilians versus strictly military targets. If Russia used nuclear weaponry as they currently use their conventional missile weaponry in ukraine I'm not sure the international community would care more than they currently care about the war, in a world where the political taboo of using nukes did not exist.
