All deposit of USDC automatically converted to BUSD.
Actually it makes thing easier for user because now USDC and BUSD always calculated as 1:1 with no swap fee. Crypto pair are more lean since they only need to pair with BUSD.
Options to withdraw USDC still available and will use BUSD balance.
You misses where Binance doing automatic conversion for any deposited USDC to BUSD. So every USDC deposit will counted as BUSD.
Withdrawal using BUSD and USDT is still available. Even USDC on some chain are still open. As I understand they just need time to replenish their USDC.