It's not necessary to reclaim every kilometre with fighting. If Russia is brought to it's knees financially, the peace can still be achieved.
Just look at ww1. For its entirety, the front was in France and Belgium and Germany held french territory. They still lost. And the Atlantic blockade and sanctions were a big part of that.
Du fragst wo?
Dort, wo die Hühner gackern und ein kleiner Kater wacht.
Dort wo Pettersson Zuhaus ist und mit Findus fischt und lacht.