Few years ago when I watched this film for the first time, I wasn't interested in knowing what he said to her at the end. I like the mystery that the film put in the mind of its audience. But watching it again and again makes me want to know what he said that gave Charlotte some hope.
What they had was special, and nothing can take that away from them. Bob may leave her physically but the memories will bring back good feelings to Charlotte like he was never away. As for Bob I think it will be harder for him as he has to deal with being with his wife of 25 years and kids again. He may be physically back with his family, but his heart and mind is with Charlotte at the other side of the world.
That's what I love about this film. They know their place in their special relationship and they never took advantage of the situation. Love can be translated and communicated in many ways. And this film touched me dearly.