The defeat will be unbearably humiliating to Russia so Ukraine can’t win as Russia sees it.
Also, having such powerful ( backed ) adversary at your border will weaken Russia with it’s nukes juxtaposition a Russian Ukraine with the ports to the Black Sea and buffer between Nato countries and the enlivening feeling of victory will strengthen Russia’s government.
I have a religious viewpoint on all of this but looking at the world as a chessboard without destroying it, Russia’s government has become less communist in the modern world and other communist countries too. Communist countries are changing towards a capitalist socialist democracy if the world economy holds up. Communism will wither away or collapse suddenly in one country after another. If Ukraine wins, it is a big step towards waning communism in Russia . The Russian government’s strenuous attempts to re-liven old ways cannot reasonably succeed because the world and the Russian people don’t want it—seems.