Return to online-only after using a file. Is it automated, or do I have to do it?

Hi,
Relatively new user to working within a team with a business account. Just trying to get my head around the finer details of working online-only. We're coming from Adobe Cloud where we've been able to use external storage and allow all files to sync locally. Love the idea of online only, as we won't be able to store everything on the local HD's due to the amount of files. 

Here's my query - for example, you open an online-only InDesign file from the local Dropbox folder in Finder, InDesign opens, relink anything where it's needed - great. When you finish working on said file and saved, is everything eventually automatically returned to its online-only state, or do you need to right click and do it manually?