The more that I think about this, the more that I realize that there is no benefit for Ambrose to win this, clean or dirty, and that the only way that both members get kept safe is for Rollins to cleanly win this.
Ambrose will always be the Lunatic Fringe, from now on. Wins won't build him or tear him down. Rollins losing, however, would severely diminish his shot at a successful cash in, and if he can't beat Ambrose, then what chance would he have at remaining the champion?
A face has to defeat Lesnar, and then Rollins will have to defeat that face. Rollins can't have a loss to Ambrose in the recent months on PPV and successfully maintain that WWEWHC steam. However, if Ambrose wins, Rollins looks weak, Ambrose looks the exact same as he does right now, and there is a net zero sum gain by having them fight.
Agreed.
But not only will Rollins look weak, but losing can cause a lot of Heel Heat he has built to be lost. After all, the whole reason he has so much overness as a Heel is because he broke up with the Shield and since then he has been pursued by Ambrose.
Indeed, eventually Ambrose will need to get the win because "Good" triumphs over "Evil" and in any case, given how the betrayal happened, the majority of fans(myself included) will always be rooting for Ambrose to get that final bit of revenge and give Rollins his comeuppance.
So basically, this match has to be very carefully booked in a way that Ambrose gets more over as a face and probably will see him come close, 'yet so far' in terms of the win.
I say best if Rollins wins and continues his momentum as an Opportunist type of heel(I mean, he just Curb Stomped Randy on RAW anyways). A clean loss for sure will cause a halt in his momentum.