I think he needs to retire. I'm ready to read his autobiography, as well as see a new documentary about his career, and finally see him in the Hall of Fame making an epic speech. It's time. I like the Undertaker, but I for one am not interested in seeing a 60-something year old Undertaker barely move in the ring one day, or worst, end up in a wheelchair. This is the perfect time to retire. Hell, the guy is already semi-retired and only wrestles once a year. If his body is starting to shut down on him then it may be time to hang up his boots and go out on a good note with his head up.
Ideally, I'd love it if he could just somehow wrestle just one more match at Wrestlemania this year and put The Rock or Brock Lesnar over - Or hell, WWE could totally fuck with the fans heads and let the fans know that it would be Undertaker's last match and make the fans think Taker is going to lose, but then he actually ends.
I would LOVE that.
I also think Shawn Michaels or Mick Foley would be the ideal choices to induct Undertaker into the Hall of Fame. Or Undertaker's long time friend Bret Hart would be another good choice. Or Paul Bearer, but I think a fellow wrestler should be the one who does it. i.e. Someone who was actually in the ring with the Undertaker and helped him make money.