#2. Brock Lesnar wins the match clean
Brock Lesnar defeating Roman Reigns wouldn't even be a surprising outcome, considering that he's done so previously. This is the same guy who defeated Kofi Kingston in a mere eight seconds, ending his WWE Championship reign.
Brock Lesnar could then move on to other opponents like Bobby Lashley following the upcoming draft. The only issue with this is that the WWE Universal Championship becomes a part-time attraction again.
#1. Roman Reigns defeats The Beast (with a little help from his friends)
This is why WWE may just choose to have Roman Reigns, their only major full-time box office draw at this point, retain the Universal Championship. But to keep Brock Lesnar, who's a box office attraction in his own right, looking strong, Roman Reigns may not win the match clean.
Paul Heyman and The Usos may conspire, scheme, plot, and ploy on ways and means to make Brock Lesnar lose the match. Roman Reigns may not come out of the match smelling like roses but whatever works, in order to retain the prized gold around the waist, right?