I've though for a long time now that RJ could be Dr Steiner.  He asks Jane to witness his suicide because he is afraid of an autopsy.  Why would someone who is afraid of being autopsied become a coroner?  Hey may have just taken a drug which made him look dead.

Also many theories say that RJ like Lisbon which is why he didn't kill her.  In the episode where Steiner 'dies' he says:

"Agent Lisbon's a good person.  She reminds me of......never mind"

He never does say who she reminds him of. 

Also the scenes with Jane and Steiner were always quite funny.  The writers could have kept him on the show to pop up every now and again just to add comedic value.  There could be another reason for taking him off the show.