I'm of the opinion that he'll be part of WrestleMania XXXI in some way, just not sure if it'll be as a wrestler. It wouldn't surprise me if Taker winds up headlining the WWE Hall of Fame Class of 2015 which, all things considered, MIGHT be the best route to go.
Taker's streak is dead, so there's no real reason for him to continue wrestling. When it's all said & done, Brock Lesnar will be the only guy who goes down in the history books as the one who ultimately got the better of Taker. Aside from Lesnar, Taker's beaten every big & legendary name to come through WWE in the past 25 years. Also, after what we saw at WrestleMania XXX, from a physical standpoint, I'm of the opinion that Taker just doesn't have it anymore. The wear & tear has finally caught up to him to such a degree that it's beyond difficult for him to put on a competitive looking match. The wear & tear has also made it more difficult to stay in shape, as if the aging process in & of itself doesn't make it difficult enough as it is, because Taker was probably in the worst overall shape I can recall seeing him. For the first time, he struck me as "old" in his appearance. He was lacking significantly in muscle tone and his cardio most definitely wasn't up to par, though, to be fair, Taker sustaining a concussion early on in the match didn't help his performance either. I respect the hell out of Taker for his work ethic and for literally trying his best but, in my opinion, he's at a point where he's not physically able to compete at the sort of level to where he wouldn't be an embarrassment to himself. The spirit is willing, but the flesh is weak. By the time WrestleMania XXXI comes around, Taker will officially be 50 years old, plus the wear & tear of the business has caught up to him with a vengeance the past 5 years or so and it's only gonna get worse as he gets older.
Of course, there's also the possibility of a match with Sting for WrestleMania XXXI. The streak is a nonfactor now, obviously, but I suppose there could be the possibility of Taker vs. Sting as nothing more than a special attraction. The match would be a novelty as the first & probably only meeting of the two most overall respected stars to debut in the last 30 years in American pro wrestling. The novelty of the streak being on the line may not be necessary because, let's face it, it was HIGHLY unlikely that Sting would have ended the streak. As we all know, Sting is the biggest star in American pro wrestling to have never wrestled a match in WWE, Vince McMahon had absolutely no hand in cultivating Sting's career or his rise to stardom and, as a result, the notion that a wrestler who succeeded and made a superstar career for himself in the United States without any association with Vince McMahon whatsoever ending the streak would be blasphemous in Vince's eyes. So, I suppose they could do the match just for the sake of the novelty of it being Taker vs. Sting. Neither guy has anything to gain or lose really and it could be a huge, nostalgic moment in the eyes of a lot of fans. The downside to this match, of course, is the genuine possibility of it completely, 100% sucking ass due to one or both men being in such piss poor physical condition that they can't engage in a physically entertaining bout.