Depends how intergrated you are. If you're using it as a code repository fine, if you're tying your workflows into it with pull requests, actions, maybe a third party CI which ties to it, and use it as part of operations then it's a major problem

I just approved a PR which added a user to one of our AWS accounts for example, if github is down then that PR can't be approved, the update can't work and the user can't access that account