If GitHub went down, how much would it impact the open source world?

Sure, there would be local copies everywhere, but for a distribution version control system, it's pretty centralized at GitHub

If GitHub went down, the code would be fine (just announce a new official URL), but the main thing that would be lost is issues and pull requests. Maybe Git should add official support for issues and pull requests in its metadata to be fully decentralized.

Fully decentralized metadata so we can finally have merge conflicts in PR comments while discussing merge conflicts

Yes, as a I mentioned there is plenty of local copies of the code floating around.

Everything else... as the original comment said, is pretty centralized for a decentralized system.

>for a distribution version control system, it's pretty centralized at GitHub

This is what I don't get ... what is the alternative to GitHub?

Linus Torvalds invented git, which is what's used by GitHub and others like gitlab.

I know that, I just didn't get this part "and 20 years later we all use it to store our code in a single place".

And as I can see here, no one else did ...