Can someone explain how proponents of the "party decides" theory think that there will not be a revolt by GOP voters if the party nominates someone who came in third or fourth place in the delegate count by virtue of votes cast in primaries?
Easy: It's a two party system and no matter how mad they get they aren't going to vote Democrat.
You're forgetting the obvious alternative - not voting at all.
Yeah, it's not often that it happens, but I agree with Wulfric here. Revolt doesn't have to manifest as crossing party lines or anything.