What makes it an archive in terms of longevity? Is it backed by governments or NGOs? What if the funding stops? Etc.
I was working in a French government-funded Web preservation project.
Many countries have such government-led projects (france, norway, iceland, italy, usa - via the library of congress, slovenia). For a full list of who does that, see https://netpreserve.org/
Short answer: partial replication of the data at other institutions + overlap of the archive at other institutions
Many projects like internet archive exist, they are not necessarily publicly accessible via the internet (in France the archive can be consulted from public libraries via dedicated computers).
If you are interested in the topic, also take a look at the LOCKSS project from Stanford: https://www.lockss.org/
- http://timetravel.mementoweb.org/ (search seems to be down)
- https://www.webarchive.org.uk/mementos/search (search not responsive for me)
- https://mementoweb.github.io/SiteStory/redirector.html (protocol and tools)
Cases are handled on an individual basis. Sometimes those exceptions apply, sometimes the needs of the individual supercedes those public interests.