The Ukraine doesn't have the geographic advantage that Russia had during WW II where they could trade space for time by retreating. If Russia invades, I suspect it's do or die for Ukraine. I don't see the EU jumping in, not after the experience they had in 1914 and 1939, but hey - what do I know.
Another way of looking at it is whether Putin wants to risk another Afghanistan. If I'm wrong about Ukraine's ability and will to resist (very possible), and Russia's invasion gets bogged down, that resurrects a lot of ghosts from 1979.
More like emotional about his Russian brothers taking his freedom away (again).