I'm hoping it won't end soon because it would be cool if he were able to break the one year mark. The last time anyone did was Cena 6 years ago. If they want to fully establish Punk as a top tier talent then a lengthy world title reign is crucial in helping him reach that status. I doubt that a year long title reign will end up happening. One could argue that Punk has had a lengthy reign already. 214 days is incredibly long, longer than any reign since Cena in 2006-2007. It would benefit him for it to last a bit longer. I just wish he closed more PPV's with his WWE Championship matches, but that is a topic for another thread.
I think that the Money In the Bank winner will be the one to defeat him. They could have him cash in on the 1000th episode of Raw, which would lead to a rather cool moment. The potential for a historical moment is there, so WWE will probably follow through with that and provide it. Or they will just end up putting the title back on Cena. We will just have to wait and see.... I'd like to hope that it will either be as a result of a cash-in at the 1000th episode due to the historical value of making a new champion on that episode, or after he has passed the 1 year mark.