You know, it's interesting. If Putin did that, and simply admitted that the invasion was a bad decision (even though he of course believes it was justified ... blah, blah, blah, ...), I think most of the world, and most Russians, would respect him for at least admitting to the error. No Ukrainians would, understandably, because they have suffered the enormous losses caused by that "mistake"; but most of the rest of the world would, I think, more or less respect the admission of it.
But Putin's ego is such that in his own mind, to admit to ANY degree or error regarding this invasion would be tantamount to admitting an abject, total failure, warranting certain termination of political power and probable execution (because that is how he would respond to someone else's similar political blunder). And perhaps he would be right after all, given the death and suffering resulting from his big "mistake" in judgment.
Hmmm ...
My contention is that the only way this war ends is with the end of Putin. He 'screwed the pooch' on this one, and he cannot/will not fix it because that will cost him his position, and probably his life. So he has to go, now, but he isn't going to go willingly. So it's up to the Russian people to rid themselves of him before he destroys the whole country in his effort to stay in power (and alive) when he has clearly forfeited the right to either.