The only way is just to cede the land and move on. Keep the people alive. 100 years later one can renegotiate. This kind of copium hope wishing the economy collapse or something like Mongol collapse is just not practical. The longer this drag on, the lesser fertile men exist in Ukraine and the population recovery will take even longer while Russian outbirth in the long run. Sometime to win one has to abide by time. Joan or Arc and King Goujian of Yue demonstrated that principle well either by divine intervention or human vengeance. Russia is doing very well. You can check with your Russians or Northern China friends that see the conditions with their eyes and not western propaganda.