I have viewed the end of your posted video several times and there is a lot going on there. At one point I think you achieved slightly over 10K feet in horizontal distance which is impressive where as I usually start to loose image transmission signal around 2500 ft but I realize it's all in the particular area you are flying. I do have to give you props (drone pun intended...Ha Ha) to ride your flight out that far. I would have hit RTH way earlier. Although you were taking a great risk running it out to such limits you should have been able to cancel the "low battery" RTH safe mode and flowned it back manually. The compass and GPS errors were several and it's had to tell if you actually lost connection with the drone and the RC. The video gets choppy and then goes black a few times then comes back. Does image transmission guarantee you have control connectivity of the drone? Guess not in this scenario. Also I'm sure the compass and GPS errors did not help the already depleting battery level.
Thanks for sharing your painful experience so that we all can learn from it...Jeff
Pushing the limits is all part of the fun. But I didn’t expect this to happen.