The outage probably isn't going to last forever. And it's very unlikely you'd need to refresh third party repos in the time github is down.
Now if you're juuuust looking for some library or its README/documentation (I usually use Github for that) ... well I'm sure going for a walk for a few hours won't hurt you :)
It's actually quite likely. If you have a git repo listed in a Gemfile, for example, and you need to bring up a new server or deploy, you're going to have problems. Sure, the outage isn't going to last forever. But the standard, snarky reply about git working fine locally is really tiresome.
Instead of a snarky reply, perhaps someone will think of a good solution.
The simplest possible thing: instead of supporting a single git URL, allow specifying several. That way, if anything goes down the system can fallback to the next git server.
Another nice benefit of doing this could be automatic load balancing.
Your statement was "If only there was some way of using git locally without needing github". Stick to it and save the theatrics. Git is a software package that you can download and use, yes Virginia, "locally". As to the availability of a remote host serving a precious resource not being available, well Virginia, those are just the facts of networking life.
