More realistically I don't see the Republican party splitting wholesale as much as we see a rerun of what happened with the Tea Party; wherein the crazy fringe was able to rile up the base enough into primarying out 'moderate' republicans and shift the whole tone of the party even further right.
That or the Fringe becomes marginalized to a nothing element of party policy because not-as-crazy republicans decide they want to maintain (at least the illusion of) power more than sticking to their whackjob ideology.