The Internet Archive would be the perfect group of folks to archive code.

Indeed. Updates in Github (which can create a webhook) should trigger an archive operation.

It has been on my list to integrate https://github.com/joeyh/github-backup with https://github.com/ArchiveTeam/ArchiveBot.

I love the Internet Archive, so it would be great if some kind of archiving function could be worked out. But if it's on GitHub now, it should be exported to Zenodo today, so there's at least one reference version around for Internet Archive to backup.