Trump will not lose unless it becomes a two person race. Even then, hes got a ton of momentum. "We dont win anymore" plays really well with "look at cruz/rubio/carson/kasich, they lose. Theyre part of the reason why we dont win anymore. Look at me, I win."

They gotta wheel and deal and promise VP or something, else its Trump takes all.

Also, the GOP wont dare swindle this away from Trump by changing the rules. The fear that he'll run in spite of that is too great.