Another source, for academic writing, is jstor.org. A lot of the older stuff is free with an account. It presents as if you need a current educational affiliation, but not so for a basic free account.

Honestly, a ton of stuff is digitally preserved. Far more than happened historically. Sure a lot of things will still end up in the bit bucket but we're still never going to preserve everything and it's probably just as well that we don't.

mostly they are. newspapers.com has 1000's of papers (in image form, not text, unfortunately) going back to the 1800's.