If Russia does lose, then that would hurt their pride and Putin's image. Russia is already in a decline and unable to hold back Western intrusions. I don't know what Russia's future will be after this tbh, they say that it might economically collapse which have been accelerated by sanctions against it.
Considering that Russia has nukes, it's possible, if Putin was that crazy and really desperate, to use nukes on Ukraine as an ultimatum if there was no other way for the Russian military to keep up with Ukrainians and as a way to flex that they are still capable.
But that would also lead to retaliation which means that U.S. might be lead to nuke Russia, and whether or not that might lead to Russia or even China from launching their own retaliatory attack on the U.S. or NATO.
It might be possible that even if Russia nukes Ukraine it might not be worth it to attack Russia if there was no further threat to NATO countries in Europe, and instead let sanctions do the work to collapse Russia's economy.
If Ukraine does manage to take back their eastern front and Russia gets too weak that they decide to just back off, then it might just stay where it was before.
I don't think China is any better than the West, tbh.