DRM-laden digital books should be seen like the extra cheap paperbacks which fall apart sitting untouched on the shelf after a couple of years. Extremely different than the well-bound books one might think of when handling a 100 year old book.

Non-DRM'd ebooks in formats which are open, easily parseable, and that people care to archive should be fine for a long time. Some people here are talking about a decade as if we won't be able to parse epubs or text files in 10 years. I've got documents >30 years old already which are still easily parsed, and I don't imagine I'll have problems rendering them in another 30 years.

I'll be utterly amazed if we can't render a basic HTML document, text-focused PDF, or hell even just ASCII text in the year 2032. I also have little doubt I'll still technically be able to load my DVDs or Blu-Rays of that data in 2032 and copy it into the holographic crystal storage devices that'll come out just before that.