I think some exchanges have notified CZ already that they will block those addresses, but I don't know if he has discussed this to some known mixers to block it as well. But it's going to be difficult to get their cooperation though. Anyways, there are a lot of blockchain forensics right now and I'm sure their hands are full trying to track everything down to the smallest amounts and where it goes.
They could do it. There were cases of exchanges blocking stolen cryptos before.
If hackers are smart they will buy monero or zcash to better hide the coins instead of trying to mix them. While CZ is doing his talking hackers could be talking with some shady exchanges like yobit to help them launder if for a hefty fee.