I don't know the answer to your question, but it seems like you think that people have more than one liver. All people only have one liver and you will die without it. Maybe you meant to say kidneys since there are 2 of those and you can still live with only one of them.
If he is turning 80, still works, has a great brain still and full of life, I would not worry about his life expectancy. It seems like he is still doing quite well.