I see quotes like this all the time, but it makes no sense to me.
The only way to win the GOP nomination is to get the most votes in the primaries.
The nominee is always the person who got the most votes from the constituents in the Republican primaries. There is not some super secret power committee who picks the nominee. The party rank and file do!
Of course, that may spur some to form a third party, but there's no reason to believe that the majority of the party they split from will follow, since they got the nominee they voted for!