Heres your answer:
Deleting accounts doesn't mess up any threads, like
this thread. It just changes to anonymous, with no profile information. Post stays intact.
As you can see here, I only change the username to "Anonymous" on request.
Some people that asked for their account to be deleted managed to get it anonymized, although it is pretty rare to see, and I havent seen any anonymized accounts that did not take place quite a few years ago.
And if you want to see another strage combination, take a look at SyphirX's case (conserves the name, tagged as guest, and profile not accesible):