This is distinct from Google saying "bye y'all, no more GETs for you" with no other way to access the data.
other readers may be specifically interested in their contingency plan
That’s not to say that DOIs aren’t registered for all kinds of urls. I found the likes of YouTube etc when I researched this about 10 years ago.
Crossref isn’t the only DOI registration agency. DataCite may be more relevant, although both require membership. Part of this is the commitment to maintaining the content.
You could look at Figshare or Zenodo? https://docs.github.com/en/repositories/archiving-a-github-r...
Then Rogue Scholar is worth a mention. https://rogue-scholar.org/
Sorry that doesn’t answer your question but maybe that’s a clue that DOIs might not be right for your use case?
It is built for the task, and assuming worse case scenario of sunset, it would be ingested into the Wayback Machine. Note that both the Internet Archive and Cloudflare are supporting partners (bottom of page).
(https://doi.org/ is also an option, but not as accessible to a casual user; the DOI Foundation pointed me to https://www.crossref.org/ for adhoc DOI registration, although I have not had time to research further)