Any progress toward peace would likely begin with a cease-fire, perhaps sometime this summer or fall, roughly along the lines of current combat.
With this approach, Russia would remain in control for the foreseeable future of most of the land it holds now — much of the East, the Crimean Peninsula and the land bridge between the two. No agreement would be reached on permanent borders. Kyiv and Western countries could maintain their principled position that all of the disputed land is Ukrainian. They could hold out hope that a future Russian leader after Vladimir Putin might see things the way they do and finally return the land — perhaps in the 2030s, once Putin is finally gone.
Until then, Russia would remain under sanctions. As an inducement to Putin, however, the West could signal that these sanctions would not get any tougher or broader once a cease-fire was reached (ensuring, for example, that Russian natural gas exports to Europe would not be targeted). Some type of international peace observation mission might be deployed to monitor the cease-fire lines while also making it harder for Putin to resume the attack (since doing so would risk the lives of soldiers from many countries, even if the peacekeepers did not have a mandate or the capacity to stop a Russian attack).