On the Family Guy panel at this year's Comic Con showrunner Steve Callaghan confirmed that a Griffin family member would perish and be replaced by a new character in the upcoming series. He denies that it's Peter's mother Thelma, who dies in an upcoming episode (possibly due to the real life death of Phyllis Diller in 2012, who voiced the role after taking over for Florence Stanley when she passed away in 2003) but verified that it would be one of the six main characters, though he would not say who exactly.
This comes as big news for the series, but it should be noted that Callaghan didn't say whether the deceased would meet a permanent demise or just be killed off temporarily in one episode then eventually return. Killing Peter would be the shows demise and Stewie, Chris or Meg being replaced by another child doesn't seem likely. The obvious choice would be either Lois expiring and Peter remarrying or Brian dying and the family buying a new dog, but I can't be the only one hoping for Brian to get sick then make a recovery; only for Meg to suddenly die.
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