Here's a test case:
webjay@6c574a6

npm run mocha -- --grep "should fail fast if repo not found"

Mocha times out, but Nodegit should fail before that.

On a Heroku instance, after a very long time, I have seen it fail with Error: SSL error: syscall failure: Broken pipe.

In rare cases I have seen a 404, so perhaps this is GitHub related.