How do you see a match up like that ending? USA pushes Russia back to pre Crimea seizure borders? Why stop there? Why not go to the Volga? Ukraine reached alm

How do you see a match up like that ending? USA pushes Russia back to pre Crimea seizure borders? Why stop there? Why not go to the Volga? Ukraine reached almost all the way to the river before WWII. Maybe go all the way to the Caspian? Provide some security for Georgia and incidentally get A LOT of oil. At what point do you suppose Russia abandons its "no nukes" policy in this hypothetical conflict?