What happens to Rubio delegates if he drops out?
If he “suspends” his campaign, they remain his at the convention, bound to vote for him on the first ballot. If he officially withdraws or officially releases his delegates, they can vote for whoever they want starting on the first ballot.
State rules apply. Some states bind them regardless, some states allow them to be free agents, etc. They definitely are in no way subject to the whim of the former candidate.