According to The Hollywood Reporter, Lincoln, who plays sheriff Rick Grimes, will exit sometime this season. It was already known that Cohan, who plays Maggie, would leave this season, since she picked up the lead in ABC’s midseason series Whiskey Cavalier. Currently Norman Reedus, who plays Daryl, is negotiating a new deal that is rumored to be north of $20 million to take over as the lead on the series.
Lincoln’s decision to exit is a shock to the brand, since Rick Grimes is the main character in The Walking Dead comic series created by Robert Kirkman and Tony Moore, and still very much alive in that continuity. However, AMC has stated many times that the show is more of a “remix” of the source material, and has deviated in the storyline several times, most recently in killing off Rick’s son, Carl (Chandler Riggs) in season 8. (Carl is still alive in the comics.)
The Walking Dead showrunner Scott Gimple left the series at the end of the eighth season to serve as the franchise’s chief content officer, being replaced by writer/co-executive producer Angela Kang as showrunner and executive producer for season nine (see “'Y: The Last Man' TV Series News, 'Black Lightning' Ratings, 'The Tick' Renewed, 'Umbrella Academy' Filming, 'Snowpiercer' Greenlit, Gillian Anderson Off Geek Shows”).