This is why a lot of companies use a product like jFrog artifactory to handle dependencies. Instead of trying to download files from GitHub and other random places on the internet, the artifactory is a local mirror of all of those files, with servers on the artifactory which run the relevant services such as a npm repo of packages, a npm repo of packages, and so on.

This way, if GitHub falls off of the face of the earth tomorrow, the packages still build. Also: If some open source maintainer deletes an older version of a package, replacing it with a new one with a different API, the local package will still build.

(The local build process will have to be set up to use the local artifactory to pull dependencies, of course.)