I'd be surprised to see Brock at this years Mania, I doubt Vince will want any other 'big' returns to take anything away from the prestige of having Rock in the main event. And Brock doesn't deserve to end Taker's career either, no-one does really.
I've said before, Taker should beat whoever he's facing, and then do his usual celebration/blue light/tongue thing. The the ring goes dark, a single strike of lightning hits the ring, and when the lights come back on, he's gone. And that's the last time we see him.
Interesting theory but I don't think they will just let him disappear. If HHH is in the rumble I can see UT showing up and pulling him out of the ring or something along these lines.