Ultimately Romney’s delegates can vote however they choose if he isn’t “running”.... Is that right?
They release their delegates. He could ask that they vote for McCain or Huckabee, but they aren’t bound to do that.
Romney didn’t “end” his campaign, he “suspended” it and is hanging onto his delegates. Most likely to give him a significant presence at the convention and input on the platform, but if something unexpected happens he could restart the campaign. I presume that people can still vote for him in the remaining states, he’s just not spending money to enhance his delegate totals.