Maybe you could still leave it up to the author? i.e. just list inactive blog entries, for how long they've been inactive, and a quick way to delete some/all of them.
Yup that could be a way to go, although I think that when you leave it so, people will just forget to get back and change such settings hover again. For quick deleting you can already do this right now, straight form the public page of the article if you are logged in(as well as per editing)