If GitHub were down for two days that's a metric shitload of projects that can't get deployed. There's a significant number of software projects with dependencies on Github-hosted stuff.
But if github were down for two months, the nature of git suggests that deployment for those many individual projects would shift either to the originators' infrastructure, or some other aggregating service.
There is a lot riding on GitHub that developers use. Hell, even closed-source companies sometimes use empty GitHub repos so they can use Issues for openly available tracking.