I agree with you regarding Putin's mindset, but with 40,000,000 Ukrainians, he simply doesn't have the military he needs to subjugate -- let along kill -- them all. And the survivors of every Ukrainian he does kill will swear an oath to avenge that death.
I'm not sure how this will end, and almost anything is possible. But anything short of leaving Ukraine entirely is going to result in Russia having to fight every hour of every day until they do leave. The Ukrainians are energized, enraged, and inspired, and they will not give up until every Russian is gone from their land.
Putin cannot win this war, at least not in any meaningful sense. And if he isn't sensible enough to realize that, let's hope someone in his inner circle does, and takes appropriate action to end this war sooner rather than later.