"27.6% of the Top 10 Million Sites are Dead"
https://medium.com/@tonywangcn/27-6-of-the-top-10-million-sites-are-dead-6bc7805efa85
"..more than a quarter of the top 10 million domains are no longer accessible. This suggests that as time passes, your history and contributions on the internet could gradually disappear."
Also:
"38% of webpages that existed in 2013 are no longer accessible a decade later"
https://www.pewresearch.org/data-labs/2024/05/17/when-online-content-disappears/