Amy, Based on my own experience and from what I have read from other posters at this site, it is clear that this kind of life event, is the mental equivalent of being hit in the head with a hard swung baseball bat. Literally it stuns a person!
Many experience depression and that affects our thoughts. Coping even if you don't have depression is a still a challenge. I have said it here before this is as much a mind game as it is a physical healing.
The plus side of these things is that it will be a learning experience that can build tremendous caracter. It has that effect not only on the person who has cancer but on many people around them. Read the story of Antarctic explorer Sir Ernest Henry Shackelton and his perserverence against all odds to save the lives of his men. Many times he might have sat down and said to his men "it's over" and he would have died and so would his crew.
What I am saying is that we have to remind ourselves that each of us can do a lot of good even if we have only a short time left to do it. Yes it is possible that even with the pain of treatments he may still not survive. On the other hand he may survive and live to positively affect the lives of many others. We all have this ability. Some go through life never knowing or realizing that (and in fact he may know it just temporarly distracted). If just living and dying on the planet was all we were supposed to do, mankind would still be cave dwellers.
Perhaps you can suggest to him that this is his chance to really make a differance in the world.