Would a compromise be to simply archive them but not make them freely availible until they enter public domain.

For more current book; if they are out of print then they can be made availbe for limited loan, like any other digital library. If a digital copy is avalible for purchase from the original publisher/author, than its not fair game. Unless they come to an agreement, perhaps add supported for freely accessing a book otherwise available for purchase.

If they got rid of the download option, it would make it much more difficult to just use a DRM stripping tool (a friend told me about these terrible pirating tools, I certently don't know how to use then). A lot of digital libraies have a dedicated app that you can only view content from. Utilize whatever anti-screen capture systems banks and Netflix use to protect from simply taking screen shots. Make is easier to access the books legitimatly than it is to pirate them.

Lastly, don't just make everything freely availible next time there's a world crisis.