 <p>I think you basically have the right idea. You should listen for collaborator leave/join events and update what is being tracked appropriately. As you say, its OK for multiple people to make the changes for leave, as they will do the same thing.</p> <p>The <a href="https://github.com/googledrive/realtime-playground" rel="nofollow">Realtime Playground</a> has an example of this.</p>