Absent evidence to the contrary, my take on Putin's actions are that he wishes to reestablish the buffer region Russia has historically maintained around itself to absorb invaders. He controls every state near him except Ukraine, so I would let him have it and then he will have his buffer and hopefully be happy. He has nowhere else to go after that except actually attack NATO, after which there is world war, so the appeasement that is possible in this case is rather limited, it really can't go further than this.

Anyway, I get the argument that you should stand up to the bully, but this guy gives me the vibe that he's actually all-in and will (literally) lose his head if he loses this war. I think if this continues and he gets into a losing spot, he will gamble that his nuclear forces will win. I don't see any other option for him actually.