I never thought that you're a statistic until you're dead anyway - then who cares. Of course if he's really old, has other health issues, still drinking, smoking, or chewing tobacco then thank him for improving MY odds.

Oh and did I add that the chance of recurrence is 80% in the 1st year and 15% in the second, then drops to 5% after that so statistically he is past the worst part.
Future tripping can only serve to drive you both nuts. Take it one day at a time. Only God owns the future. Tell him to have some gratitude for what he has TODAY - that he is cancer free! Maybe he needs some therapy.

I'm in the same place, at 2 years, and the same stage III/IV and except for when I'm visiting here or someone asks me about it. I don't think about it much anymore. I have moved on and life is fuller and richer than ever before, every day is a gift.