[oldcynic]

Well, if it was published it was deposited with the national library - British Library or Library of Congress. I think other nations have similar systems. Covered newspapers, magazines and books. The British Library page:

https://www.bl.uk/aboutus/legaldeposit/introduction/

"By law, a copy of every UK print publication must be given to the British Library by its publishers, and to five other major libraries that request it. This system is called legal deposit and has been a part of English law since 1662.

From 6 April 2013, legal deposit also covers material published digitally and online"

[WalterBright]

What happens when the Library of Congress, or the British library, burns down? What happens when the Vatican library burns down (a large part of it consists of unique documents with zero other copies)?