What are some that should be archived by numerous users? I'm thinking more information-heavy sites.
Sure, The Way Back Machine might contain them, but even they might one day be bankrupt or shut down
https://archive.org/details/the-hitchhikers-guide-to-online-...
It's on Archive.org but as you said, even that could go defunct.
I'm also worried about quite a few older gaming resource sites that seem like they could go away at any moment. Like VG Maps (the ads are already ridiculous, and I suspect it's not making a ton of money anymore) ad VG Music.