[plugnburn]

The advice is simple: Don't rely on third-party stuff you can implement yourself with no significant effort. And for stuff you can't, backup those modules.

[jonahx]

What is the best way to backup modules? Do you need to create your own private module host, as you can for ruby gems?

[plugnburn]

I may sound old but one can start with just backing up node_modules/ directory.

If third party modules are hosted on GitHub, you can fork them.