Maybe you can have them switch the repos to public if you go through their support, but Github doesn't offer that in their ransom note, and that would be an unacceptable solution, anyway.
Whether or not this is a risk to a given developer (or their company) is irrelevant to me, because they still have policy that allows them to hold code hostage for ransom, and that should make Github a complete non-starter when deciding on an SCM host.