He would go nuclear in a heartbeat. He may even be considering it now. He would see it as justified revenge against a world that would not let him have his own way.

He is not a normal human being. If he had one bit of respect for life, he would not be bombing residential neighborhoods with a vengeance right now. He has no soul. If he can't have his way he will destroy the world.

That said... NATO should be giving Ukraine more weapons capable of shooting down high flying Russian bombers. They have already orchestrated a deal for Poland to give jet fighters (the type that Ukrainians know how to fly) to Ukraine, for just that purpose. They should be arriving soon if they haven't already.