You could, but in all honesty, most programmers (myself included) aren't as brilliant as Linus Torvalds, and, while I could stand up a git mirror in my sleep (because it's trivial - you should be able to as well), the finer points of coordinating work via a git mirror, when https://xkcd.com/1597/ is the level of understand most people have with git, seems to say it's not going to work. Add on the fact that the git repository is the least bit of functionality (eg PRs and pipelines), and being down is a serious barrier to progress.

http://Xkcd.com/303 but for GitHub is down.