At this time, word is that the decision to wrestle at WrestleMania 29 is being left up to The Undertaker. WWE obviouly wants him to work the pay-per-view but also feel that he has earned the right to decide if he feels he is physically up for committing to a full WrestleMania storyline and match.
There is also talk of possibly just using him for a Royal Rumble appearance if he doesn’t work WrestleMania.
