Just try and be yourself and go with flow according to your friend's mood. He's probably still trying to come to terms with the news himself and will probably be suffering violent mood swings between anger, depression, frustration and fear. But if he's a close friend and wants to talk about his death, try and have the courage not to skirt round the issue. It's about coping with his needs and not worrying about your own discomfort dealing with uncomfortable topics. I remember a terminally ill friend saying to me "Everybody wants to help you to live, but nobody seems prepared to help you to die", and sometimes this is what people want and need, in terms of emotional support, helping them to reach the right frame of mind in coping with what's to come.