Hearns either by stoppage or points. As defensively gifted as Whitaker was, you can't rule out him seeing the final bell, but Hearns has all the tools to put him away if the opportunity presents itself.
Hearns would be looking at a man smaller and weaker than Duran, whom he called a midget. Benitez was not a natural JMW, if you look at where he was at age 25. Where he was as a teenager means nothing. Nada. He's still growing there. Benitez, at 5'10, is naturally stronger and bigger than Whitaker and has comparable defensive skills. And Benitez had underrated power. What does Hearns do with Wilfredo? He boxes him. Against Whitaker, I think it likely that he would show two faces. He'd come out slugging to test his theory that little men can't stand up to him. Then he'd be missing -lots, and would adjust. He'd box him at range and try to measure him... and lose a few of the middle rounds. Eventually though, he'd find that range because he would apply serious pressure. I don't see Hearns getting winded because Whitaker is not going to have the capability to do to Hearns what Leonard did. Hearns would find him and hurt him late. He may even catch him early. If he does, Whitaker is going to be in real trouble because Hearns hit harder than Zeus. I'm not convinced that Whitaker's evasive prowess is going to be enough at this weight and the fiery Hearns was three times the stress of that automaton Felix. Would Hearns stop a pudgy Whitaker? 70/30 says he would.