I'm happy to report that this project is no longer needed, you can solve the problem of disappearing nodejs modules by swapping npm for yarn.

Backup node_modules for all your npm based projects.

$ npm install npm-rescue -g
$ npm-rescue

Follow the instructions for finding your npm projects and creating a local git repo to backup your node_modules directories. Each project is backed up to a different branch.

Backup your modules any time by re-running

$ npm-rescue

Forgotten where your local git repo is?

$ less ~/.npm-rescue/npm-rescue-config.json