Yes, as answered in another branch, it's possible and reasonable to setup continuous / daily backups, if you're using a hosted Git service (Github or not). This will mitigate the risk of losing access to the code.

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.

You don’t understand - there is no need to setup backups. Every user has a full “backup” of the repository (unless using sparse checkouts or other niche configs).

It really depends on how small or large your organization is.

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.

This is true for the source control aspects of Git, but not all of the project management aspects of GitHub. (wikis, gists, gh-pages: yes. issues, pull requests: no)