I'm on the vendor bandwagon; always have been. I don't want a github outage to dictate when I can build/deploy. Yes, that happened. That is why we vendor :).
Now you can set up a proxy server; however, I don't want to do that. I'm pretty sure I have a few vendored packages that no longer exist at their original import path. For code reviews, we put off checking in the vendor path til the end if possible.