All pledged delegates (which is over 90% of them) are required to vote for their state’s primary winner on the first ballot by law. Federal law. Under penalty.
This story is yet more smokescreen by wishful Cruz/Kasich supporters. It just isn’t going to happen.
Again, Trump will win the first ballot with or without the required delegates. If he’s slightly under it won’t matter.
I think the bigger picture is that this would completely destroy any confidence and trust people have in our elections. Once that happens who knows what’s next...