With the exception of cuneiform text on sun-baked clay tablets, most ancient writings have disappeared because they could not withstand the forces of nature. Animals and plants die, and their bodies and fibers deteriorate. Since most writings prior to the digital age were placed on sheets made of animal skin or plant fiber, most have turned into dust. Even more modern paper has been ravished by insects and acidic inks. I think writings will have a much better chance of surviving the eons to come if they are digitized. Assuming there is anyone around in a million years I doubt they will find many, if any, of the non-digital writings of early humans. And yes a million years from now we will be considered "early humans" in the literary sense as writing has only been around for a few thousand years.

Unfortunately the quality of writing seems to be on a downward trend what with all the blogs, websites, texting, emailing, etc. But that has little to do with libraries and a lot to do with the ability of anyone who owns a computer, smartphone, etc. to become self-published. In the era when publishing meant ink on physical medium, most people never got published, thankfully. Today anyone can get published and most seem to, though most seem not to be literary geniuses.