If this happens, Cruz needs to instruct the delegates he owns to vote for Trump. Not sure if that can happen? Larry?
I don’t think so. Pledged delegates are often bound by law, not by the candidate. Of course, if you violate that, who’se going to come after you? A district attorney? No.
There are a couple possibilities, but, in general, no candidate can give binding instructions to any delegate.
Cruz could release his delegates and probably count on enough of them to switch to Trump, providing they check to see if enough states allow delegates to be released.
A safer method might be to go to convention and use the combined Trump-Cruz majority to change the rules, again providing state rules are taken into consideration.