His thought-to-be grandson Lennox, who's immortal like he was, replaced him in the same episode.
He came back though, in the episode Time for Another Ghost Hunt as a ghost, but before Ghost City's destruction, he permenantly died after sacrificing himself to The Ghost King.
Tyler was thought to be Lennox's grandfather, but Lennox revealed in the episode Time for Another Ghost Hunt, that was a false fact and that they were just acquaintances.
The episode For a Spin revealed what caused his death was strong chemicals that Stephanie accidentally spilled on some green iron oxide, TNT and a boron flame and before the lab the team investigated in exploded, which removed most of his skin and severly burnt him.
His death in Time for Another Ghost Hunt, was also caused by an explosion.
He stated once that ghosts can be destroyed by explosions.