The user who was doing this has not been active on the site for a long time, and to the best of my knowledge, no other users have been attempting to do it.
My suggestion: We allow the self-delete in general. If any individual user is found to be abusing it, per-user permissions (or perhaps just a special permission group they get added to, preferably an invisible one if that can be done) could be used to override this and revoke their ability to delete their topics.
I would not consider it inherently "abuse" simply because they delete a topic with replies, provided it was not done for a malicious purpose (such as hiding criticism). Users should be encouraged not to do this as a "mini-mod" type thing; ie: if there are a few legitimately problematic posts in an otherwise-good topic, they should not delete the whole topic to get rid of those posts, instead, they should ask a mod / admin to remove just the offending posts. We have an extremely high mods-to-regular-users ratio, so it shouldn't take long for such posts to get dealt with; and most problem posts on this site have been harmless-but-annoying spambot posts, nothing particularly severe.