They are buying back rouble like crazy, they burn billions of dollars per day in foreign exchange
Well, given the sanctions they might as well burn these dollars/euros. So maybe it's not that bad to pump their currency rate here.
So, I think they can move their yuan freely to China still, but USD and Euros are harder to move (though not impossible?) in China
If Russians stop accepting rubles and use foreign currency for transactions, the Russian govt stockpile of rubles, and it's ability to print more rubles, becomes worthless. They will need foreign currency to pay people.