In CP, you can delete his account and you have two options regarding his posts
Warning: Deleting a member can not be undone.
-Do not delete this member.
-Delete member and do not alter posts. Ownership will be set to Anonymous with an Anonymous name of: [user's name].
- Delete member and delete all posts. If there are any replies to a post by this member, they will be attached to the post's parent. If the user's post is a topic, the entire topic will be deleted.
At least, that's how it works in 7.2.2.
As for deleting all of his posts in one fell swoop, but not his account, I'm not really sure.
Maybe someone else can step in and answer.
I'm guessing it can be done via MySQL.
