Arducopter does have failsafe (hover) feature like if agriculture spray is empty . When spray content is empty the drone should stop at same place and gcs should indicate that spray tank is empty.
User can take control and land safely and refill the spray content and mission should start at where it left at last flight.
You could probably setup a Battery Monitor input to perform the failsafe action you want. You will have to condition the output of whatever sensor you use to be in range of the configurable options.