How to have nodes online but not as a separate node number?
You can't disable the node entity's canonical path easily, but you can serve a 403/4 for requests to the pages instead.
The simplest method for that is probably the Rabbit Hole module

Rabbit Hole is a module that adds the ability to control what should happen when an entity is being viewed at its own page.
Perhaps you have a content type that never should be displayed on its own page, like an image content type that's displayed in a carousel. Rabbit Hole can prevent this node from being accessible on its own page, through node/xxx.