Russia might not nuke for a small border incursion (they've shown themselves dickless in that regard time and time again) but basically all the mineral wealth that makes oligarchs rich is east of the Urals. So obviously they would use nuclear weapons if that was going to be lost.

Who would win? the rest of the world since China would have 200 million plus of their population turned into crispy shredded beef and Russia would be basically destroyed.