I would listen to him, if he felt like he wanted to talk about it, but if he wouldn't talk about it, I would try to keep our friendship as it was before. There is no reason to talk about the death, when he is still alive, and you can do things together. I would of course try to arrange things he has been dreaming about. It could be a one-week travel to some place, bungee-jump, or something similar.
I think most people with life-threatening diseases want to keep their life as normal as possible, instead of all their friends and family are worried about them, and don't really know how to handle the situation.