Eventually Putin will die. Maybe he'll keep power until his deathbed, maybe there will be a coup and he'll be removed and/or killed. But one way or another, eventually Putin will die. When he does, this insanity can end.
I don't know that it can end from anything short of that.
History does not support this, unfortunately. Russia has always been aggressive towards outside world and invaded its neighbors multiple times. Putin is just the latest in a long string of aggressive leaders.