Currently, when the user is online we open Google Drive files and similar in browser, and the browser can redirect the user to the Drive app if needed. At the same time, we download a copy if the file in background. When the user is offline he can open a downloaded copy if there's any.
It can be confusing for offline users to open an outdated copy of the file, we should improve the UX so the user knows exactly what will happen. Ideally we should also try to launch the file in the Drive app instead of browser, but I think it won't be possible.