#3 Wyatt Family members attack
This is one of the two ways WWE could avoid having one of the two men lose the match. It would allow neither Bray nor Seth to take a pin-fall, while having WWE technically not go back on their word.
If Wyatt Family members (new or old) were to interfere and drag one or both of the men out of the arena, the match wasn't stopped, it simply could not continue. It's a Falls Count Anywhere match, which inherently means there are no rules. Therefore that doesn't rule out interference. Whether it's Harper, Rowan, or both -- or even someone new from NXT, or possibly even one or multiple people in masks (Fiend masks, perhaps?), if one or both of the competitors were to be carried away, or, even better, suddenly disappear, then the match can't continue.
The idea may seem like a cop-out or going against what seems like a promise that there will actually be a finish, but WWE is absolutely not promising that there will be a conclusive winner or loser. The wording of the stipulation lends itself to interpretation. It "can't be stopped for any reason" seems to mean that the referee can't call the match off. It can end by traditional means or, on the exact opposite end of the spectrum, it can end by extremely non-traditional means.
The complete disappearance of the competitors ostensibly means the match is over. And because it's not in front of a live American audience, they can really just do what they want.