Ukraine can't win in the sense of achieving an outright battlefield victory and ejecting the Russian invaders. But NATO and the EU can keep Ukraine from losing by continuing to support them, and maintaining sanctions on Russia. This will bog down the bulk of Russia's expeditionary military capacity in a quagmire, just like with Afghanistan in the 1980's.

Unfortunately this will have some bad effects for the rest of the world in terms of food supplies, but it's a price worth paying to eliminate Russia as an effective geopolitical player for years to come. Remember that it's not just about Ukraine. If the rest of the civilized world pressures Ukraine into ceding territory to Russia as part of a peace settlement then next year Russia will try to take a little slice of Poland, a little slice of Estonia, etc.