This works similar to the Realtime Database in that it's last-write wins (where in the offline case, "last" is the last person to come back online and send their write to the backend). This model is very easy for developers to understand and directly solves many use cases, especially since we allow very granular writes which reduces the risk of conflicts. But for more complex use cases, you can get clever and implement things like OT conflict resolution as a layer on top of last-write wins, e.g. similar to how we implemented collaborative editing with www.firepad.io on the realtime database.
PS: Hi Chris! :-)