[taspeotis]

Well if you're only using GitHub for hosting the repo then you can still work with your copy of the repository while GitHub is offline (since you're in distributed not centralise version control territory).

Git has a file protocol so you can also just sync your changes between one another via a network share of your repo. Or SSH or email each other pull requests.

[raindev]

Right, just communicate directly with your colleagues when GitHub is down. This is exact workflow Git was designed to work with.