Sounds all right.
Have Undetaker lose again, maybe even lose some of his dark mystique and all that, and give it to Bray.
Undertaker disappears until next year, then comes back to take on someone else, and everyone is talking about how he's past his prime, lost his power, the fans don't even really want to see it...
...and then at Wrestlemania...a glorious victory, he kneels down, does the tongue and eyes, lightning bolts, and then lies down in the coffin never to be seen in WWE again.
Who he would face I dunno - if you gave some parts of the Undertaker gimmick to Bray, then i dunno if you should take them back off him, but that might even be a dumb idea anyway. Bray needs more threat about him but it doesn't have to be taken from the Undertaker. So he could come back and beat Bray a year later after Bray has a year of terror, during which time he builds lasting legitimacy as a tough guy and spooky fella.
Undertaker shouldn't lose his last match, I don't think.