Assuming the npm registry doesn't dissapear, npm will download the exact same files you would have committed to your repo
I think that’s where you missed what the gp is saying.
If everything is checked in to source control, npm will have nothing to download. You won’t need to call npm install at all, and if you do it will just return immediately saying everything is good to go already.
The workflow for devs grabbing a 10 year old project is to check it out then npm start it.