Although guilt is common during grief, it should not be hung on to. No one in the world is a perfect wife, son, grand-daughter, etc...All you can do is use that grief to learn from and then let it go. Guilt takes up the space in our heads where honor, peace and good memories are. I certainly would never want anyone to feel guilty upon my death. I would want them to look to the skies and say "it was really great knowing you". You and your grandfather shared more good times than bad times; remember the good ones.
btw; I really like this "If there is no God, who pops up the next Kleenex"