>>114599353It's a complicated situation: the voice actor was one of the American Dad writers, who got moved to Family Guy when Seth ordered Family Guy swap writers with American Dad (due to Family Guy having a run of god-awful seasons while American Dad undergoing a golden age of high quality that forced Seth to order such a huge shake-up of outright switching writing teams).
The plan was for him to continue to voice Terry, but then Fox canceled American Dad and when it moved to TBS, Fox flat out refused to allow the guy to continue to voice the character since he was under contract for Family Guy as a writer due to the switchover.
So they wrote Terry off by having him abandon Greg to be a groupie for the 90s band 311. Though he had a non-speaking cameo in the 200th episode.