(But) no one has ever finished a zombie story. This is potentially due to the fact that it would be a curious mix of horribly uninteresting and horribly depressing if it did happen, but it's still a worthy thing to wonder about. Hell, George Romero has spanned four movies (more if you count things like Diary of the Dead, which you shouldn't) and decades of time and still hasn't gotten to the logical conclusion of all zombie fiction -- the end of humanity. If zombies kill everyone, then what happens?
Land of the Dead was just ridiculous, and the best it could offer up was walled-up cities and the decrepit countryside full of undead people in costumes and one ridiculously crafty zombie gas station attendant. But if there was a World of the Dead to follow it up, would it literally just be zombies standing there? Is that the end result of the zombie apocalypse? That's the worst end of the world ever -- a planet of guys loitering around drooling black stuff on themselves and occasionally moaning at the breeze.