That is a possibility especially if it's a RINO who feels they are entitled to be President. I don't know if their are any out there that are quite that bad. I don't think even McCain would pull the party that far down. He didn't in 2000 so I don't think he would now.
No, it'll be someone we don't suspect, possibly someone most of us aren't aware of. How many were aware of Perot when he first showed up on the scene? He can be manufactured and manipulated.