I voted "No" in that it's not over if Trump wins South Carolina.
Trump is not considered an acceptable candidate for the GOP Establishment. How they feel about him vs. Cruz is up in the air somewhat, but his nomination is viewed by the Establishment as a bad thing for the Establishment, and for other GOP candidates in less-red states. If he wins South Carolina, the Establishment will then have to come to grips with the fact that they will have to coalesce around one candidate, or deal with a Cruz or a Trump at the top of the ticket, because Cruz is going to finish second.
I'd love to be a fly on the wall of Reince Priebus's office after the South Carolina results come in. You can bet that he'll be on the phone to anyone and everyone who can pressure the 4th and 5th place finishers to drop out. Because that's what's going to happen. No dinosaurs made it through to the age of Man and no Trump Deniers will make it though South Carolina.
Reince is a good friend of TRUMP's. TRUMP thanked him in his NH victory speech.
The Establishment absolutely hates Cruz and will pick TRUMP before Cruz any day of the week and twice on Sundays.