Is it possible to run React project without npm start?

For those who are getting 404's after deploying in a sub directory. Make sure to add the path in package.json as homepage.

"homepage": "https://example.com/SUB-DIRECTORY",

It is absolutely possible to run a React app without a production node server. Facebook provides an easy-to-use project bootstrapper that you can read about here

That being said, developers may need to use a node dev server locally via npm start, as well as using node to perform production builds via npm run build. But one can take the build output from npm run build and serve it from any static server and have a working react application.