I would think smart RTH would work in that case. The Mavic will travel as far as it can keeping in mind how much battery is needed to get back to home. This would really be testing the range of the battery and not the aircraft/signal though. Also, as others have said smart RTH is a rough estimate and you could end up with a forced landing before it gets home (at critical battery level). Keep in mind that RTH is supposed to be a backup in an emergency so it is not meant for normal use and your mileage may vary.