Is there a communuty project that maintains a copy of the 500k books? Is there a libgen torrent or anna's archive torrent?
If you are upset about this, commit to seeding as many of these as you can until the IA service is restored.
Very different sets of books. I don't see how this will help. LibGen isn't going away, not that I'm aware of.
IA is mostly full-color scans of old library books.
I've never come across an IA scan on Libgen. Libgen is mostly EPUB's, native PDF's, and the occasional black-and-white high-contrast PDF scan.