If the forum gets hacked again, then who knows what will happen with the data which was compromised. It'll likely get sold and eventually surface in the public eyes for free.

How likely is it that the government will request your information? Unless, you are caught breaking the law and up on trial it's unlikely that they would send a request. The above link was major news around the crypto world. It's probably the biggest subpoena that theymos has received to date. If theymos does receive a request to release data on you then it's down to his discretion.