Professor Lupin is something of a novelty in that he is the only
Defence Against the Dark Arts Teacher to appear willing or likely to ever return to
Hogwarts. We are told this towards the end of
Harry Potter And The Goblet Of Fire when
Professor Dumbledore instructs
Sirius Black to 'alert the Old Crowd' including
Remus Lupin,
Arabella Figg and
Mundingus Fletcher. As he was arguably Harry's favourite teacher at Hogwarts and much liked by
Readers Lupin's presence in the as yet
Unpublished Harry Potter And The Order Of Phoenixwould be a welcome and popular
Plot Development.
Lupin is probably the most likely Dark Arts teacher to make an appearance in future volumes of Harry Potter. First Year Teacher Professor Quirinus Quirrel(played by Ian Hart was a host body for Lord Voldemort and apparently died upon disentegrating when he touched Harry. Second Years' Gilderoy Lockhart (played by Kenneth Branagh in Chamber Of Secrets) fell foul of his own Obliviate memory charm and is Amnesiac. Lupin resigned his post after longtime rival Professor Snape revealed to Slytherin students Lupin - as the english translation from Latin of his surname suggests- was a Werewolf. Fourth Years' Mad Eye Moody was only employed for one year "as a favour to Dumbledore" (is there a Temp Agency in Diagon Alley?) but spent most of his tenure locked in a chest with an evil impostor (one Barty Crouch) assuming his identity to kill Harry.
It is fair to say that none of the above will be taking their old jobs back and Lupin, being friends with Harry's late father (James Potter) and fugitive Godfather (Sirius Black) has a vested interest in Harry's safety. Wether or not Lupin turns up in Harry Potter books to come will remain the topic of discussion among Potter fans and will be a development watched with keen interest