Eventually, all series end, and the sort of unacknowledged built-in, self-cancellation timer is the premise of the show; its a world overrun by zombies, so once the horror of that is no longer a novelty (and that's been gradually happening the past three or more seasons), all you have left is that quasi-feudalistic system with the enemies (Woodbury sort of worked like that as well as the Savior's system) and tribal war. That's not "survival horror" anymore (the original point of the series), and with that, the series should reach some natural conclusion. AMC, Kirkman, Hurd, et al, may not have the stones to actually bring it to an end. It may take one of the leads to want to move on (as in not moonlight on other jobs, but really break free) to force hands.
Kill off Michonne and Carl? I do not see the series doing that, although Michonne's "its your show" (paraphrasing) line to Carl almost hints that when Rick is away, she's not the leader of Alexandria, but prepping Carl for that role. Who knows?