They could still do things with Rock, Sting and Brock
Rock - face Reigns at Summerslam/WrestleMania to pass the torch once Reigns is over enough as a main eventer, face Brock in their rematch from Summerslam 2002 at a WrestleMania, face Orton (should have happened at WM XX) third generation star vs. third generation star, face a heel Cena - finally break the tiebreaker between the two.
Brock - face Orton - Brock never faced Orton in his prime, face Reigns in a WrestleMania rematch, face Rock in a Summerslam 2002 rematch, face Cesaro.
Sting - face Taker, face Rollins
since when does the wwe bring back a part timer and book them as a heel ? Besides Brock, its obvious why he must be booked heel . Don't count Batista, they had to turn him heel last year because he was blatantly and genuinely being laughed at. They want to make money( i.e. sell merch to the kiddies ) from part timers like the rock and sting.