You answer my questions first. It might not be; not convinced it is.
No, I can't query a deleted account other than indirectly. Every account has a unique number (it's just a counter) and when the account is deleted, the number is lost. It won't be reused but you can't tell who it belonged to.
As for posts by deleted members, you may have noticed that the posts are authored by named guests. The setup is the same as it was when guests were allowed to post--the post is associated with a name that is really just a character string that is not associated with anything else than that particular post. Searching for posts by that deleted member simple gives you a series of unrelated posts where the named guest happens to use the same alias, every time. You can't use that to search for quoted replies other than by inference.
The quoted posts, on the other hand, display the nick used by the member at the time when the post was made. Again, this is similar to the guest setup. It's just a text string that once was the member's then-current nick.
All of the relations have been lost, see. Every single one, really.
There is an option to delete that member's posts when deleting the account, btw. There's no way I'd agree to anything like that because it would fuck up the db. I doubt the code would be able to handle a forum as large as this one, not if the member in question had posted more than a handful of posts.
ponds from now on.