To be honest, I don't anyone has ever posted a
complete fanfic, and I'm fairly sure no-one will.
However, in this situation, I'd consider having to wait for a long time to pass for the thread to dissapear to be far too long a wait for someone that deserves comments, in which, say after a certain amount of time, say one/two weeks (enough time so that comments could have been posted) then I'd allow that member to create a double post to get their thread some attention, but I'd say that these cases are rare.
If however, this has happened to you, and your thread from a
long, long time ago has been forgotten, I'd say reposting the thread is fully justified.