I just realized recently the best way to master a good bye is to take control of it. When you know good bye is about to happen then YOU be the one to conclude the session, say it was awesome to see / be with you, say that we'll meet again, and then end etc. Good bye is questionably more important than the whole interaction. A bad good bye can completely 180 an amazing interaction. A good good bye can leave her thinking of nothing but you until you call and she picks up.