Why are people so worried about how a potential loss will make Brock look? Even if he loses, when he shows up on RAW, people will still cheer for him. Worried about him looking weak? Simple fix. The commentators play up how tough he is for even being in the UFC, hard battles, training, etc. Then Brock smashes the first person in sight. Hell they could even use it to his advantage. He loses, snaps, storms the ring & goes back to beating the shit out of random people like his old days.
Then they pick one guy to stop the beast. Instant mega push. A UFC win or loss still equates to an experience notch in his belt & a resulting big rub for the one to dethrone him in WWE. Let's be honest. Brock is nearing the point of one's career when they are going to be asked to take a loss or two on the way out. Randy wont be one of the few to beat Lesnar.Despite his return, a loss here wont hurt Randy & the beast slayer cred would be wasted on him as opposed to another.
All in all, I doubt the UFC outcome determines who takes the SS match.