I've just been reading @TidyDancer's thread, which popped up in Active Convos today, which was started back in 2011. (Feels like only yesterday 
!)
Several posts have been deleted, at posters' requests - presumably they deregistered for some reason, and then asked for everything they had posted to be withdrawn. But it leaves the thread a bit 'holey', and disrupts the conversation/narrative.
Instead of deleting the posts, would it not be possible to just delete the usernames? You'd probably also have to have some kind of way of deleting any mention of said usernames too, as replies might make it obvious who had made the post. But it would leave the thread much more intact.
Now that Cod has learnt to spell/type properly 
it's unlikely that anyone would be able to identify who the poster was, I think.