I do think the GOP will have to try and club together now to manufacture a brokered conference.
But even if they achieve that Trump is likely (unless he loses next week) to be there with a huge backing, so not choosing him would smack of the kind dictatorial elitism that massively damage the party.
That said, if Trump is the ticket and runs Hilary close, that brings into question the electorates view of the GOP base.
So the only result that won't fundamentally change the GOP is Trump losing the presidential election by a large margin.
I think we'll see Hilary beat Trump by appx 58-42% with many purples voting to keep Trump out rather than Hilary in.
And I do think you'll then end up with a political landscape where the GOP is somewhat like Labour - one badge, a million different factions.