Third, if the Rules Committee provides no alternative to Rule 16 and no minority report with a conscience clause is sent down to the delegates, a majority of delegates could still derail the Trump train by voting against the Rules Committee report. In that case, lacking a set of rules from the committee, a different set of “temporary” rules from the Tampa convention would govern the Cleveland proceedings, and those rules do not include a Rule 16 analogue binding the delegates.
Fourth, the longest of long shots exists where a majority of delegates approves a Rules Committee report that includes being bound a la Rule 16. In that circumstance, holdouts opposing Trump could potentially force a second ballot by having several hundred delegates abstain from voting on the first ballot. Most delegates become unbound after the first ballot owing to the interaction of Rule 16 and state party rules, meaning a second (or later) ballot could theoretically have enough votes to nominate a candidate other than Trump.
This final scenario is most unlikely for two reasons. As a matter of logic, if a majority of delegates were willing to nominate a candidate other than Trump after the first ballot, the same majority would presumably have voted down any Rules Committee report with Rule 16 and dispensed with being bound from the start. Moreover, as a matter of practicality, the nomination is typically done by voice vote, and it would have to be a very large group of delegates indeed to convince Priebus that sufficient delegates had abstained on the first ballot to require a second.