Oooo, I’m guessing a lot. Particularly with more and more books being published in e-pub formats.
There is a problem, though, with stuff being stored exclusively or primarily on the internet.
For starters, what if something happened to destroy the internet? How would we reassemble all that date? Could we reassemble it? Another issue is format. Files that could be read or run 10 years ago might not be usable now, or in another 10 years. I know I don’t buy books on kindle type formats that I know I’ll be using for years (like my knitting books) because I know that a book will still function, but my ability to access and use a kindle file might not.
It’s an interesting question, and we do need to future proof ourselves. I know I rely an awful lot on the internet and my computer. If I lost them I would have to completely change almost every aspect of how I work and play.