I haven't checked GitHub specifically, but most of those terms include, "and we can ditch you any time for any reason, maybe with 30 days notice if you're paying"
Not to mention it's also common to include "we can change the terms at any time" - and of course, there's also the fact that this issue in specific has nothing to do with a ToS violation, but with permissions on the parent repository, by relying on them with no backups you're not only subject to their staff's whim, but to the whim of any bugs or "features" in their code.
If you want to take advantage of their infrastructure, that's fair, I understand, but at the very least, run some tooling to backup issues, pull requests, wiki pages, etc on a regular basis.
I haven't checked GitHub specifically, but most of those terms include, "and we can ditch you any time for any reason, maybe with 30 days notice if you're paying"