For Iowa its even else:
"[...] Another astute question FHQ has received concerns that Huckabee delegate. And now that Rand Paul has also withdrawn, another delegate can be added to that mix. What happens with those delegates?
They stay bound to Huckabee and Paul regardless. The only out for Iowa delegates is if only one name is placed in nomination at the convention. If only one candidate is placed in nomination, as has been the case throughout the post-reform era (save one contest, the Republicans' first under the new system in 1976), then all of the delegates are bound to that candidate.
Unlike some other states, Iowa does not permit the release of delegates nor for them to become unbound in any way.[...]"
http://frontloading.blogspot.de/2016/02/the-iowa-delegate-count.html