The premise doesn't make a lot of sense.
> monetary sanctions because they are in EUR or USD
Yes, because that's what the contracts specified as a currency. Russia uses the ruble as a currency, which is not censored, it's just not 'in demand'. Adopting BTC how? Do you think Germany et al would be willing to pay for oil/gas in bitcoin when the contracts already specify a currency? Or adopt BTC internally? Like all the babushkas fighting in line for sugar would need to have crypto wallets now?
Also, wallets of Russians could be denied transactions.
Also, BTC is small enough to be manipulable by an alliance of state actors if push comes to shove.