Notch is a slick man. He knows how to program games like a stud and he went on at least one John Carmack-esque programming binge and came out with a new game in under 48 hours. Mr. Minecraft also knows how to subtly tease people, and the best way to do this is to not address a pink elephant, strategically of course.
In one of his latest tweets, he asked for writers to help with text in which to pop up once Minecraft is “won”. However, Minecraft is a game that is notorious for not having a goal, but rather asking the player to create one on their own. Though this could be a misconception, as what most people have experienced as Minecraft was, and still is, in fact a beta.
So Notch has all but explicitly stated that Minecraft is going to have an ending. Where Minecraft would have to lead to make such a dynamic shift in game theory has yet to be seen, so be sure to tune in.