I always believed the writers deliberately left the door open for Petofi's possible return....how ironic it would have been if Petofi HAD been the one [spoiler]Professor Stokes went to see about exorcising Gerard's ghost, and considering he still had scores to settle with Barnabas and Quentin....I could see Petofi (putting on an act of an angel of mercy to the professor), instead of exorcising Gerard's ghost, actually aiding him in destroying Collinwood and the Collins family. That would have been Petofi's ultimate revenge against the Collins men for outsmarting him back in 1897.[/spoiler]
Now THAT would have made a great twist.