If we operate from this principle, it becomes a lot easier to solve the conflict.
On a sheer economic and logistical perspective, the war is taxing, but if the alternative is losing face, is a leader who has always burnished an image of strength going to be a Rational Economic Actor?
Putin has to deliver something of a win for his domestic audience. So frame negotiations around the smallest prize that would let him walk away looking like a winner. Give him a white elephant like "you don't want Ukraine in NATO? Fine, here's a defence treaty that puts the cost of defending them on your budget." as long as the elephant has a big ribbon on it.
But is the goal to pragmatically end the war ASAP or enforce schoolyard "the bully cannot be rewarded for being a bully" justice?