If they do not support Iran, and America wins, they lose not only cheap Iranian oil, they lose their One Belt trade route too, say nothing about unlocked American Navy, which might try to intervene while they are returning Taiwan. So, they may support Iran to continue war, or can invest more, but proxy-win this war against America. And if they win - and America leaves Middle East, it might worth a lot. Their potential victory in Middle East might even create a new reality of petro-yuan for China and some kind of "gas OPEC" for Russia.