I wouldn’t think of it as that. The funds wouldn’t leave the mint’s control. Course funds in the maker offer, while waiting for a taker wouldn’t be available for immediate withdrawal. So a mint would likely have to keep a reserve of UTXOs not offered for coin joins. I think withdrawals could be handled by withdrawing non offered funds first, and then rescinding the offered funds if needed. Keep the questions coming! We were just spit balling over lunch.