Deleting a user* but not
 

We've got a user on a site that has asked that all of their content be removed. Now I generally honor those requests promptly* as the site has a policy that the content belongs to the users. Of course that means that all threads started by the user disappear as well as all posts made in other people's threads. For a normal user* this is generally not a problem* but this user is what you might consider a "power user". Many hundreds of threads that the user started* and many thousands of posts in other people's threads. Overall effect on the board is going to be about 40*000 posts if I just remove the content and delete the account by the time you consider that all of the threads started by the user will be removed.

I'm still going to comply* but staff has asked me that rather than handle it the normal way which might normally affect half a dozen threads and a couple of dozen posts* to just delete all of this user's posts so that the valuable content from other users that were in threads started by this user can be salvaged. I'm fairly competent with SQL and have no problem with deleting every post this user ever made in a single query* but what I'm struggling with wrapping my head around is how to delete the user's posts without orphaning the threads that the user started.

Any advice?