My heart and prayers go out to you, sir.
It seems that your grandfather led quite a full life and made an impact on those he encountered. Our lives pass so fast and our memories so short the best one can do in their life is to make the lives of those around them better. By the sound of your post that was his legacy. Some men are only remembered by a name or a photo as succeeding generations grow older, it looks to me like your grandfather, despite his own failing memory, will be remembered for the life he led and the great impact he had on your family.
Don't be too somber, my brother. Life can only be appreciated if there is a distinct end. His has arrived. Do like I did my own father. Tell him you love him and wish him a cheerful departure. May God bless you and your family.