Both Andrew Lincoln (Rick Grimes) and Lauren Cohan (Maggie Rhee) have expressed they are no longer fulfilled with the direction the show has been going and the decisions taken by AMC and previous showrunner Scott Gimple; and will be leaving the show by the end of season 9.
AMC claims the show will go on.
It is rumored the demise of Chandler Riggs (Carl Grimes) was a major factor on Lincol's decision.