If a third of Trump voters don’t vote GOP, the GOP has no chance to win.
Ron Paul voters alone sitting out in 2012 were more than enough to make the difference in a number of battleground states, which - had these voters been given something to vote for - would have changed the result of the election. The GOP’s cynical institution of the “Ron Paul Rule” - which had no effect other than to prevent his delegates from giving him the honor of having his name placed into nomination, knowing the result was predetermined - singlehandedly lost the election.
Likewise, anti-globalist Trump voters would have nothing to vote for with a typical GOP nominee, making that an election-losing move.
The GOP has two real choices right now: Trump or lose. All other suggested potential outcomes are pure fantasy.
There is a third option, but only with Trump's and, to a lesser extent, Cruz' consent. They would both have to endorse a third candidate. I don't expect it to happen. I expect a complete rout of the Republican Party, with 12 million illegal aliens voting as new citizens after President Clinton appoints several new Supreme Court Justices with a Democrat House and Senate. I expect the confiscation of firearms and the forced acceptance of homosexual marriage by all religions except Islam as a civil right. Wickedness will rule in the United States until the coming of the Messiah.