There is one proper way to book "The Fiend" Bray Wyatt vs. Seth Rollins at Hell in a Cell on October 6: as a complete squash in which Rollins drops the universal championship to Wyatt. Anything less would severely damage the past six months of effort Wyatt has placed into his character.
A squash is typically a match involving a jobber wherein one wrestler is hopelessly outmatched by his opponent; done properly, a squash gets the winner over as an unstoppable, unbeatable force. A debuting monster heel will squash an adversary with ease before taking on a credible threat to his dominance.
Squashing is the quickest way to get a wrestler over. But WWE rarely books a squash on the upper card because of how damaging, reputation-wise, it can be for the loser. Even if the squash is sold as a fluke that only happened under extenuating circumstances, it's an uphill battle to convince the audience of that. WWE runs a risk of telling the audience it didn't see what it saw.
But there is a way that a squash can work narratively in a main event spot. For example, John Cena lost to Brock Lesnar in a squash at SummerSlam 2014 after getting suplexed 16 times. But he did not suffer any damage to his reputation because he was such a respected and established performer. The shock of his loss dominated the post-match conversation. Ironically, the rarity of the loss forced commentators to focus on Cena's accomplishments.
Lesnar's real-life legitimacy also protected Cena. As a Division I athlete and a former UFC heavyweight champion, Lesnar is as real as professional wrestling gets. The squash is rendered less embarrassing because Lesnar could squash anyone in the locker room; nobody can gloat or bury the losing wrestler without indirectly burying themselves.
For a brief, flickering moment, Bray Wyatt is over as a legitimate, dangerous threat. It took him a little more than three minutes to defeat Finn Balor at SummerSlam, where his arsenal of moves included a realistic neck snap. Wyatt has been kept off television, which adds to his mystique and ensures that he remains fresh.
But as with every wrestler, the shock will wear off. Wyatt will never be as a frightening as he is right now. And Rollins, meanwhile, can take a lopsided loss. He is the newest member of an elite group of wrestlers who beat Brock Lesnar cleanly with no interference or cheating necessary.
Between now and Hell in a Cell, Rollins should lose the psychological war against Wyatt; we should get the impression that he lost the match before he even stepped into the ring. And following the match, Rollins can disappear for a while and rebuild his confidence until he finally conquers Wyatt in a high-profile match (perhaps at WrestleMania).
Wyatt needs to remain elusive and otherworldly. A back and forth would only serve to humanize him. And any offense Rollins gets in will make his comeback, months from now, much less impressive.