This is all speculation and possible spoilers as I've done some detective work regarding to The Undertaker and Triple H.
I have stumbled upon this year's Summerslam poster which has Triple H and Undertaker prominently in the center. Also the PPV description reads, "WWE action slams into summer as John Cena, Triple H, Rey Mysterio, and all your favorite WWE Superstars battle for WWE gold and glory on Sunday, August 15th, live on Pay-Per-View!"
Undertaker being in the poster could mean his return at Summerslam after resting his nagging injuries. Triple H being in the poster and mention in the PPV description makes it seem that Triple H is also set to return, as he has also been away recuperating.
As I said before, this is all speculation as PPV advertisements are made well in advance and it could be very likely that the poster and descriptions were made before Triple H and Undertaker had each taken a hiatus.
In other words the poster and PPV description could just be misleading.
Let's for a few seconds take the information stated above as fact. They both make their return to Summerslam. I have a few theories and predictions on how they would return.
Undertaker could reveal that it was CM Punk and his Straight Edge Society who put him in a coma. The other possible outcome is that The Undertaker could come out and say that the Straight Edge Society is innocent and announce who really attacked him whether it was his own brother, Kane, or Rey Mysterio.
With Triple H, there are a few story lines that could play out. He could be reinserted into the title picture and continue his feud with Sheamus by interfering with his title match at Summerslam, if he is still champion. Triple H could be the savior of the WWE by feuding with the entire Nexus, or he is reviled as the true leader of the Nexus thus making him a heel.
Triple H could even be reviled as the secret General Manager of RAW.
The possibilities are endless for the cerebral assassin.
Whether the Summerslam poster and PPV description are clues on Undertaker and Triple H's eventual return to the ring or just mistakes to misguide fans into thinking that they will return at Summerslam remains to be seen.
Regardless, it would be a good idea to be a little more alert while watching RAW and Smackdown as to see more clues on whether the duo will return at Summerslam.