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.