The scenario where Putin loses in Ukraine is Russia being so screwed up by serious sanctions that there is regime change to something more moderate.

Sanction hurt both parties.

They also allow Putin to steal assets from Western countries that are located in Russia. The don't create moderation but basically make political life for every moderate in Russia harder.

But, as was well-covered elsewhere, the West lacks both the coordination and the moral spine to do serious sanctions.

I'm not sure whether from a moral perspective the kind of resources it would take are a good bargain. The task for a moral imperative to do something in a situation like Darfur is much higher than Crimea.

Russia lost the Cold War, remember, because it did not have a functioning economy to stand on its own and compete in e.g. military spending against the West.

At present when Western states are at the brink of declaring bankruptcy the Western strength is different than it was at the end of the cold war.