Now, I know mods can delete someone, but you need a single button that allows them to simultaneously delete the person and delete all their posts. I suggest a "Delete - With Prejudice" button. In addition to the delete function, you can have it run a query to find all that user's posts, and return the reference numbers to an array. Then, you can simply execute the "delete post" function on each posts, by the reference number stored in the array.
What do you think?