If you think conservative Republicans will be enthusiastic about Trump, you're living in a dream world. You would see volunteering for his campaign at record lows for a Republican candidate. The party as a whole will cheer wildly if Trump is defeated at the convention. Most of Trump's supporters are crossover Democrats who we don't want in our party anyway. They will only water down the platform into an anti-Christian, anti-freedom, pro-socialism message.
Cruz cannot be mathematically eliminated until June 7th. All of the unbound and Rubio/Kasich delegates are up for grabs on the first ballot. If they all go to Cruz, we will not know until June 7th if that is enough to put Cruz over 1237.
Florida, my home state, had a closed primary.
Donald Trump crushed both Ted Cruz and Marco Rubio in that primary.
The same has been true for several other closed primary states.
Thus, your assertion is fallacious, ludicrous on its face, and amounts to aught but feeble propaganda.