NavList:

Using battery operated receivers when there is a failure of the primary plotter is a smart move.  Even when there is limited power available, the secondary receiver can be switched on a few times a day to correct the DR plot as required.  Certainly this method of sailing would allow you to make a good landfall and is a perfectly legitimate method of navigation.  I carry 3 GNSS receivers powered by battery when I am at work on my ship, so that if the ship's systems were destroyed in some sort of disaster, I would still have a method of real time positioning.  

Of course if there was a systemic failure of the space aspect of the system, this method would prove to be useless as any receiver would be out of service.  Here is where Celestial navigation would come back in full force, provided the tools were available onboard.  Unfortunately all of the radio navigation systems for ocean navigating have been decomissioned. Of course the probability of a systemic GNSS failure is too small to be of any real concern.

Jeremy