How does information survive millenia?

I've recently started to read a lot of history, especially older books, and it makes me wonder how many books from antiquity never survived. There are rumors that the books that have survived from ancient Greece aren't even the best. What does it take for a book, or information in general, to survive multiple millenia. Back in the day you hand copied books onto newer paper. Right now publishers make newer printings every few years. But what about the digital information. How will it survive. Obviously, it's easier to copy the information now than back in the day. CD's may not last decades, but the storage capacity of whatever we use is increasing so rapidly that every few years (or at least every decade) you can pretty much copy all of your older media onto much fewer pieces of the newer media. I'm pretty sure I could copy every single 5.25" and 3.5" floppy that I have onto one or two CD's. And I can fit most of my music, in a high quality mp3 format, onto a few DVD's. If I copy my information every few years onto the newer media I'll have a good chance of keeping it for a long time. But of course, I'm only thinking about decades. What about centuries or millenia? If paper is stored properly it can last a very long time. But, what happens to all of our information that is only stored digitally? Of course, if we continue to copy it to newer media, and we are able to have multiple copies stored all over the world (which doesn't always happen because of people hoarding their data but that's another conversation), and we stay technologically advanced then I think we're safe, and if in 800 years someone wants to watch Saved by the Bell they can. But what happens if we have a technological dip, or another dark ages? What happens then? I don't think it's completely unfounded to think that it may happen again. I'm not one of those crazy survivalists, and I believe that the world is on the average becoming a better place, evolving if you will, but this has happened many times before. It wasn't a continuous forward movement from the Golden Crescent to Classical Greece to the Renaissance to now. Can the digital information survive another dark ages, or even a cultural dip. And if it does survive how will people ten thousand years from now understand it, obviously they won't be speaking anything related to english...?