HBK returns for a match against HHH at Wrestlemania 29? He had to end his career due to a Wrestlemania 26 main-event and now he returns to face HHH (who he has faced in HIAC, LMS, Unsanctioned Match and 3 Stages of Hell, basically everything WWE has to offer)? It's not impossible but it would make no sense at all. Top of that WWE doesn't need HBK for WM 29 since it has a list of megastars piled up for the PPV (Lesnar, HHH, Taker, Rock, Cena and Punk).
How I can see the Wrestlemania 29 PPV from here and mostly how I would book it from here is simple (only exception if something major happens):
Rock vs Cena 2 for the WWE Championship as the main-event: Cena turns heel by costing Rock his World Title match against Punk at Royal Rumble. Rock takes his revenge by eliminating Cena from the Royal Rumble match. Cena wins the WWE Title at Elimination Chamber and this sets up the match for Wrestlemania 29 where Cena continues playing heel and retains.
Taker vs Lesnar: This is not hard since WWE plans to save Taker vs Cena for WM 30 which is the right decision. Taker will win against Lesnar, even though this match/feud ended in a HIAC but it's been ages and Taker was a regular main-eventing biker back then. Taker vs Lesnar is a dream match to many fans at this point.
HHH vs Punk in a No Holds Barred Match: This needs to be done again. There is no better/bigger opponent left for these two at Wrestlemania 29 so why not book them against each other. This time the feud should be more intense and get more buildup with Punk playing the heel. This should be a No Holds Barred Match. Even though HHH is very likely to win this one, it will still be Punk's biggest match ever and help him big time. This has the potential to be the best match of the night.
Randy Orton vs Daniel Bryan for the WHC: Simple booking, Bryan wins the Rumble and challenges then champ Orton for the belt. Bryan gets the surprise clean win at Mania to establish himself as a solid main-eventer. Should be a good match. Bryan would probably turn into a face after winning the Rumble or at least during the buildup to this match or during the match itself.
Rest of the card is a filler:
Sheamus vs. Dolph Ziggler: These two main-eventers don't have anything else to do, so why not book them against each other in some sort of a decent match instead of wasting them in some random tag team match.
Rey Mysterio vs. Sin Cara: WWE is already planning this and I am satisfied with this. Even though this is a dream match of a sort but it will be overshadowed by the main event matches.
Probably there will be one more match, maybe a 6 men or 8 men tag team match or a MITB match or just a Battle Royal involving other major names like Del Rio, The Miz, Barrett, Rhodes, Sandow, Ryback, Kane, Bigshow, Cesaro and Christian.
Add in one Divas Title Match or Tag Team Titles match as the 8th match
Should be solid overall card.