10-24-2016, 08:29 PM
My guess is that Rick dies in issue #200 of the comics (would be published in 2020), and Carl is revealed as the main character. This could be a good place to end the TV show, it gives them 3-5 more seasons, depending on how they write it. I don't think they can keep JDM as Negan for more than 2 or 3 seasons, he's probably the highest-profile actor they have in the current cast. I can't see many in the original cast and crew wanting to go beyond 12 seasons on such a physically demanding show like this.
So far, there's been no indication in the comics or TV show since they introduced Eugene that they are interested in exploring the zombie virus and potential cure. I would not be surprised if one day they just discover that babies are being born immune. That would give them 8-16 episodes to wind the show down by killing off the remaining zombies and making lotsa babies.
Of course, the zombies aren't really the main threat right now.