How are the GOP brains going to stop him? He has threatened the GOP with riots. Even if they exceed with an establishment candidate, Trump will run third party. His rabid supporters will follow him.
For starters, unless Trump amasses an outright majority of delegates before Cleveland, he'll never be the nominee. Even then I believe that the GOP establishment has the will to change the rules of the convention to pull an outright Screwjob.
As for Trump running 3rd party, that has no relevance to what you stated. In fact, it's the antithesis of your claim of Trump being the face of the GOP.
Trump will be the Face of the GOP. Whether he is the nominee or not, he will be the Face. A funny face, but the Face.