I would probably quit reading if you took any of them out of the series. I like Kay and Bentons relationship and how he looks out for her. He seems to be her rock.
Let me be clear about this: I LOVE the Scarpetta series. I own and have read (not to mention RE-read) most, if not all of the Scarpetta books. However, I think that Benton Wesley is one of the most wooden, off-putting characters I have ever seen.
Lucy and Marino are marvelous, and they belong in Scarpetta's world. There were times when I liked Benton, but overall, I don't think he adds much. He may be rich, gorgeous, and elegant, but he adds very little depth to the stories. I have never really cared for him, and I wouldn't mind much if he faded out of the series. I recall that Kay was devastated when she thought he had been murdered, but I think she would have eventually recovered from her grief and moved on with her life. She is a very resilient person.