That works for the repo, but not issues, pull requests, wiki pages, permissions, or any other services GitHub provides. None of those work offline, and while there is an API that can help with migration, doing so still requires setting up a totally different system, and there is no natural backup on every developer's machine like with the repo - you have to do it manually while the origin is still up. (Not that GitHub is likely to disappear anytime soon, but all things will end someday.) Which is unfortunate because it seems like a missed opportunity: it's certainly possible to implement all those things in a decentralized manner, and some projects have tried, but so far with little success...