From what I can tell from a quick look on the wiki, Johnston was fired after season 11, his last episode being season 11 episode 19, “Bridge Over Troubled Rudy,” after which the character was absent for several seasons, then recast as Eric Bauza in season 14 (which I believe is the most recent season at the moment), in particular season 14 episode 5, “Bully-ieve It or Not.”