Answer
Our best suggestion is to keep a paper copy (ROD) of the logging you've done from the moment the device stopped updating your logbook so that the driver or administrator can update them accurately later.
If you are driving through an area with no cellular coverage, any logging done during that period of time will be updated in MyGeotab once the device is back in an area with cellular coverage.
Manual duty status changes should still work just fine for drivers who are putting themself ON, OFF, or into SB.
Additional Notes
Drivers will not be able to log in or out of the app during this time