If anyone wants to come up with an equally (or more) thorough explanation for their prediction, and I'm down for a sig bet. In other words, no "I think it's Mac because he's pissed about his humming birds." No guesses.
I'll take that sig bet. My prediction is that it is Mac who walks out. I think he is going to get pissed about something, and opt out of fighting in the semi's. I think he is actually scared to fight Arroyo because he has discounted the other fighters in the house the whole time. He seems to consider George the only half-way talented fighter in the house. The rest are inexperienced punks to him. He probably sees that Arroyo is a serious threat to him, and he will not want to take the risk of losing to him. Of course if he does walk out, he will NOT admit to being afraid of losing to Arroyo. My thought is that he will find something to freak out about, and say something about how he can't stand being around them anymore, and he is so beyond their level that he can't surround himself with such nOObness. His ultimate goal will be to get out of that fight and make people wonder, "MAN, if Danzig stayed in, I bet he would have won the finale and everything." The UFC will undoubtedly let him come back to prove himself. He has proven himself on the show already by dominating both of his fights. The UFC will want him back even if he pulls a douche-move like that. I do not doubt Mac's mental strength. In fact, I believe this is more of a mental game than anything. He sees a threat, and he probably sees an easier way to make it in the UFC. If he feels Arroyo will beat him, why tarnish his career on the show when he can come back later and fight in the UFC anyway?
This prediction is pretty out there, but I have grown pretty confident in it, even if it is a stretch.