It’s also conceivable that Putin will take a gamble on Ukraine and move in if China chooses to act.

I think from what I've read he prefers soft power methods in Ukraine. He's spoken recently of the concept of united Russian people which includes Russians, Ukrainians and Belarussians. Invading Ukraine proper outside of the Eastern provinces would be all risk and little reward for Russia and Putin, whatever you want to say about him, is a pragmatic leader.