Hello, My Grandfather, Who Is 85 Has Recently Learned That

Hello, my grandfather, who is 85 has recently learned that he needs both legs amputated because of poor circulation. He said no to the surgery because the doctors told him there was a big chance that he wouldn't make it through the surgery. Now his toe has died and fallen off. I think that he has gangrene. I was just wondering what his life expectancy would be as he is not treating any of his ailments?