While his story arcs were mixed, his standalone episodes tended to be quite good. His way of playing body horror for laughs, such as Cassandra being a bit of skin on a frame or the Slitheen wearing fat people, would make a brilliant light hearted story early in the series that would also fit the more horror-focused Moffat ethos. While Moffat keeps trying to get him back to no avail, when he left the series the first time he held on to the Sarah Jane Adventures like it was a severed limb, so its fairly obvious that hes got an addiction and gets withdrawal symptoms. It's probably only a matter of time.