YSK there is an Wayback Machine browser extension that helps with dead 404 pages and can automatically archive pages
Why YSK: Wayback Machine https://web.archive.org is an Internet Archive project that archives webpages, allowing them to be preserved in cases where they change or disappear. You can select an oldest or newest archvie of the page, or go to the list of all available archives. This helps with "dead" pages that have been deleted or old websites that have been sold to another party (including "This domain is for sale" moments).
Additionally, there is an option to automatically archive pages if they haven't been archived yet (or if there hasn't been an archive in X amount of time, configurable), meaning you can directly contribute to web preservation.