#3 Rey Mysterio interferes in the match, resulting in a disqualification for Velasquez
Or maybe Rey Mysterio does indeed return to the match to assault Brock Lesnar. This will be an easy out for Vince McMahon and the WWE Creative team especially if the final objective is to keep the title around Brock Lesnar's waist.
Things became very personal indeed when Brock Lesnar assaulted Rey Mysterio's son the first time around, which led to Cain Velasquez stepping into a WWE ring for the very first time. And then when it happened for the second time, it became amply clear that injury or not, Rey Mysterio wasn't going to take the insult and will probably assault Brock Lesnar in the middle of the match.
Because you do not need to justify an angry father who's just seen his son get assaulted, it could even get a big pop from the WWE Universe to see Rey Mysterio sprinting down the ramp to exact revenge and retribution. And this could lay the seeds for a Rey Mysterio vs. Brock Lesnar match that could happen on a stage like WrestleMania 36.
Brock Lesnar loves working with smaller opponents and the match will be quite intense.