Thankfully git is a distributed VCS. You just push the latest version somewhere else.
It's not advised for these Iranian developers to use any Github-specific features, such as issues, wiki, CI, because losing them will cause disruption / knowledge loss.
And then the reason to use Github specifically, instead of something else is quite low.
If it's a single repo with a single branch, sure. No need for explicit backups.
If it's tens of repos with multiple important branches in each, then it would be very dangerous to assume that developer machines have all of them.