ArchiveTeam is trying to brute force the entire URL space before its too late. You can run a Virtualbox VM/docker image (ArchiveTeam Warrior) to help (unique IPs are needed). I've been running it for a couple months and found a million.
* as long as humanly possible, as is archive.org's mission.
Us preserving digital archives is a good step. I guess making hard copies would be the next step.