Once he is president, Republicans will be defending him, and his ideas will get plenty of mainstream exposure. He'll no longer be the voice in the wilderness, he'll be the face of the nation. You're also discounting the follow-the-leader mentality within the party.Who is in his camp? Does he get along with Boehner? Anyone? Is he isolated the way he appears to be? My perception is that he is a long time insider who is very much alone, pushed to the outside edges.
The big thing that also hasn't been mentioned is the revolution of ideas that could happen. His platform would get plenty of exposure and people will be considering ideas that they've never heard before on the corporatist news shows. Libertarian principles will be legitimized and would hopefully lead to a (larger) movement of people willing to follow his lead and adopt his platform.