I kinda wonder what the scope of this show is going to be anyways. Like how many seasons are they planning on? Clearly at this point, they're not in danger of cancellation, so they probably are going to have to choose when to end. Personally, if the quality remained consistent, I could probably watch this show for a very long time.
But maybe there's a point at which they will be satisfied with this story? Like maybe Rick dying or something. I don't know what their ultimate goal is, but I'm guessing the ending is not going to be the end of zombies or anything happy like that.
Well the Comics/Graphic Novels are apparently quite a bit ahead of the TV Show, and still going strong, and audience for the TV Show continues to grow (Despite losing 10 Million possible viewers for the Season Premiere due to Dish dropping AMC), so, I would imagine as long as ratings continue to increase, or don't drop considerably (They were pretty excited to break the 5 Million mark with Dish viewers in S1, I believe) they'll probably keep it going, unless the Actors become too expensive for the ratings. The way it's looking now, I wouldn't be surprised to see it continue for at least another 3 more seasons.