If he ACTUALLY becomes a disciple of Red John then that would be an amazing Series Finale and honestly would blow me away. Or if Lisbon had been the plant in the CBI this entire time and Jane ends up catching Red John. The only way the show could conceivably pull those scenarios off though would be to end the show afterwards.
As it stands they are either going to do the exact same thing they did at the start of this season, he does something incredibly bad and then somehow gets away with it and everything is all fine and dandy, or something like he joins Red John and the show turns into the reverse side of the coin, him doing bad shit (Honestly I think I would be ok with that.), or something incredibly asinine that I hadn't even considered. The first scenario would be a complete slap in the face. I mean I could suspend disbelief that he would get away with murder because of the circumstances but something else just as bad a second time? That's just stupid.
I dunno, I'm going to remain fairly frustrated until next week's episode and possibly until the next season depending on how they do this. I can't see them doing something as ballsy as what I suggested and so that means they are going to do something horrible instead.