You are deluded if you think that Putin can be reasoned with. His control and power is dependent upon his image as a strong man, protecting mother Russia. His support is already fraying. If he were to lose the Ukraine War, or even another significant chunk of territory, it is quite likely that he would be removed or killed. The vultures are already circling. You cannot reason with an autocrat who is unwilling to move off his imperialistic vision.

Plus, you fail to understand that any kind of peace agreement at this point that allowed Russia to retain any of the illgotten territory would just be a pause to allow Putin to rebuild his military and try again. Not only Ukraine would be at risk. Poland, Moldavia, Finland (which the hawks are already demanding be invaded) and other countries would be as well. The countries who are most resistant to Russia in the current war and are providing the strongest support to Ukraine are the neighbors who abut the Russian border. They have a reason to be worried. Not every head of state can be reasoned with. Putin is one who cannot be. Your desire is a pipe dream.