You are forgetting that the same rules apply to Trump. Trump does not retain all of his first ballot-bound delegates, either. Trump will see more desertion of "his" delegates to Cruz than vice versa.
I’m not forgetting anything. We’ve been told the number of delegates that Cruz has perhaps picked off for the 2nd round of voting. It isn’t nearly enough.
So, in your opinion if neither can close the deal on the 2nd ballot, they will lose even more delegats on the 3rd ballot, then who will settle it?