The Undertaker's streak has become too powerful of a force. I've actually considered it being a mistake that the creative team booked Shawn Michaels and Triple H as The Undertaker's most recent victims, as Michaels and Triple H are, kayfabe-wise, two of the most successful wrestlers of all time. The Undertaker defeating them, twice respectively at that, has created a fine line in which only major stars are capable of believably ending the streak, and like it or not, CM Punk is nowhere near as successful as Michaels and Triple H. Despite what Punk has done concerning Paul Bearer and the urn, dirty tactics are mindgames aren't enough. Punk will make a great attempt, as I'm expecting several false finishes and moments that actually have the audience considering the end of the streak. But I highly doubt WWE will give Punk this big of a victory. There's only one man credible enough to end it. John Cena.
Cena's accomplishments alone are enough evidence that he could actually end the streak. He's a multi-time World Champion, he's young, and he's the face of the company. It probably won't happen (I'm expecting The Undertaker to retire with the streak intact) but it would not surprise me if Cena ended it the way it would if Punk ended it.