Rollins winning both matches would not make him a hero....based on his arrogaunt character it would make far more sense if that just fed his ego and made him even more un bearable. Rollins is clearly patterned after the vintage Horsemen era Ric Flair or Evolution HHH model of a heel champion, talented, tough, but cowardly and a cheater. When he does turn face he will have shown enough skill that it is easily believable he can win clean against top competition. Simply giving him a clean win (or two) doesn't make him a face though, it makes no sense given his ego driven presentation to think his character would suddenly become a rule abiding "good guy", if anything it would make far more sense for such a win to make him even more of a selfish heel.
Furthermore, why would HHH turn on Seth if wins both matches, clean or dirty ? The Authority are rule breakers so if Seth cheats so what, plus HHH wants to hold Cena down and stop Sting's momentum before he gets going, which Rollins beating both would do.
Personally, I think it is way to soon for Seth to turn....there is a lot more storyline with him playing his heel persona, especially if he drops the World Title to Sting, which not only emboldens "The Vigiliante" making him much more a threat to HHH/Authority it pretty much washes away the aura of HHH's Mania win over "The Icon". Put Rollins & HHH in the position of chasing the title for awhile.
Meanwhile, we never got a full fledged Rollins-Lesnar feud - Lesnar lost the title thanks to a MIB cash in at Mania, The Authority suspended him to protect Rollins, eventually he was reinstated but his lone match one on one vs Lesnar was interrupted by Taker, a return and subsequent fued that immediately tied up Lesnar and distracted him away from the title chase. Lesnar should start pursuing the title, forced to go through Rollins to get it. This is a great way to continue making Rollins seem like a legit star, he wins at Mania, feuds with Cena, feuds with Sting, feuds with Lesnar, all established main stream stars with mass appeal, with an impressive title run wrapped around it and some great individual matches.
if they want to turn him face they can do it easily by having Lesnar beat him which would catapult him to #1 contender and upset the HHH/Authority, widening what ever rift exists between them.
Rollins should lose both matches at NOC - it's time for The Authority to go take a few set backs and let the good guys take the driver seat for a bit, it's a crowd pleasing change of pace, keeps storylines fresh, and keeps all the main players involved.