Wikipedia advises its editors to backup their citations with an archive service.
Editors are also encouraged to add an archive link as a part of each citation, or at least submit the referenced URL for archiving, at the same time that each citation is created or updated.
Given the problem of broken links, I think it would be a good idea if Stack Exchange also advised users to use an archive service like archive.org to backup the links they post in questions or answers, so people can still check out the websites by themselves in case the link gets broken and see a context of the information of that website that the user posts in the question or answer. Maybe even add a tool to help in that.
Related questions:
Use Archive.org for links in answers?