At the end of the movie Fahrenheit 451, we see a colony of "human books." These are people who have memorizedbecome, so to speakclassic books. We also see them passing this knowledge to children, younger "human books." They exist and make this effort, because they live in a society where books are banned.
The purpose in describing this scene is that we're already living in such a society. We are, not in terms of books, but in terms of people. People? Yes, people. Of course, people are not actually banned, but death is an effective ban on their immortality. Not so for books, which (unless banned) have a good chance for immortality. Yet, people whose immortality is banned by death do survive, in part, because they live onin other people. Just like the scene in Fahrenheit 451, we (the repository of humanity) tell the stories of no longer available friends and relatives. And pass them on to our young.
However, people need not disappear, nor live on in such a haphazard piecemeal fashion, dependent upon all-too-human memories. The Digital Immortality Institute suggests there is a better waywe call them digital personas.