The streak IS Undertaker. It's what he's know best for. And I can't see it being taken away from him, especially when, in my opinion, he'll be retiring soon and expecting an induction into the Hall Of Fame.
I think you're discrediting Undertaker just a little bit. His streak isn't HIM persay. Its a singular part of several, bigger things, that make up his legend. Even in losing, it wouldn't hurt his legend, it'd just end with a note next to it, saying "not perfect." lol
If anything, I see Taker being inducted into the Hall of Fame for several reasons.
1.) His ability to hold a character for as long as he has, & make it still incredible to see.
2.) His wrestling ability, & history in the business.
3.) The Wrestlemania streak, broken or not, noone else has went that far unbeaten, & thats history alone.
If, by some mirical this did happen, I can envision it in two scenarios.
Either to a youngster, at Undertakers discretion, who has an outstanding amount of talent. What a feat that would be. To end Undertakers unbeaten streak. However. no youngster is going to beat Undertaker, so this is extremely unlikely.
As long as by "rookie" or "youngster" you aren't refering to Cody Rhodes, or D.H. Smith, then I'm fine with Taker dropping to an up-in-coming talent. lol
But yeah, if Taker does ever lose.. I doubt highly it'll be to a rookie, or upstart. Taker would cleanly drop to a rookie on a regular t.v. show, or probably any other p.p.v., but never at Wrestlemania, I wouldn't imagine anyways.
OR to an awfully talented wrestler such as Shawn Michaels. He may feel he only wants to lose at 'Mania to an opponenet with as much talent as him. However I can't see any of these wrestlers needing to beat Undertakers streak as they all have their own records and achievements.
I think your love of Shawn Michaels is pushing you to believe he'd be capable of beating Taker on the Mania stage. Believe me, I feel, believe & KNOW he could defeat Taker & that Taker would likely even be for it.. but Michaels would have nothing to gain, just like Taker would have everything to lose.
Whomever is going to defeat Taker, will use that first defeat to sky-rocket themselves into a solid spot, forever. H.B.K. has had a great career, with tons of achivements that'll allow him into the Hall of Fame. Again, much to some people's dismay.. I highly believe it'll be Edge who ends Taker's streak, IF it ever ends. I think if Taker remains undefeated this up-coming Mania, he'll go one more year & be done.