The delegates are bound to the candidate, but the candidate can release them from their oath. If Cruz did so with the desire they vote for Trump, some might not, but considering Trump will be within a couple of hundred of the 1,237 goal and Cruz will have 800+, releasing them would give Trump the easy win on the first ballot.
I will have to go back and research the rules later when I have more time, but it is my current understanding that the vote of a delegate who is “bound” to a candidate is recorded for that candidate on the first ballot regardless of what happens prior to the vote. Delegate who are “unbound” can vote as they please. Most delegates are “bound”.
Excerpt from rule 16: (2) For any manner of binding or allocating delegates under these rules, if a delegate (i) casts a vote for a presidential candidate at the national convention inconsistent with the delegate’s obligation under state law or state party rule, (ii) nominates or demonstrates support under Rule No. 40 for a presidential candidate other than the one to whom the delegate is bound or allocated under state law or state party rule, or (iii) fails in some other way to carry out the delegate’s affirmative duty under state law or state party rule to cast a vote at the national convention for a particular presidential candidate, the delegate shall be deemed to have concurrently resigned as a delegate and the delegate’s improper vote or nomination shall be null and void. Thereafter the secretary of the convention shall record the delegate’s vote or nomination in accordance with the delegate’s obligation under state law or state party rule. This subsection does not apply to delegates who are bound to a candidate who has withdrawn his or her candidacy, suspended or terminated his or her campaign, or publicly released his or her delegates.
It appears your analysis was in line with the rule. Hopefully it will not come to this but if so, it would be better than any other alternative.