WWE has a poll on their website right now asking the WWE Universe if they think Roman Reigns will retire Taker at Mania.
The choices for the poll are
Yes. The Big Dog will end The Phenom’s in-ring career.
No. Reigns may win the match, but it won’t be the end of The Deadman’s career.
No. Not only will Reigns not end The Undertaker’s career, he won’t win the match.
Last year it had been reported that Taker did tell some people backstage that he was done, but later changed his mind. WWE hasn't added anything special to the Reigns vs Taker match. If they do end up adding a stipulation, then it will indicate that Taker will likely call it quits and retire.
Go and vote here