Arnold's only going to get a minor slice of votes on the hard right -- some small evidence of that you see right here on these threads. That's true whether McClinock is in the race or out.
Arnold is only threatened by McClintock if the center (his center) is too small to overcome the left. It's hard to imagine any instance where Arnold could cobble together the center and the hard right. Neither will tolerate the other very well -- they're very apart on nearly everything. As long as he stays in the center, he'll only get so many on the hard right anyway, it'll be some but not a huge amount and a McClintock exit probably won't boost those numbers tremendously anyway.
Arnold's salvation has to be in the center...and his people have to be calculating that the center is big enough to do the job for him.