I usually fly with my as a carry on luggage. You may want to firstly check with the airline that you are flying with. Generally, you should be allowed to carry on and with two spares from the flymore combo should be safe. Had no issues in my travels so far. No one really. Others except for if it...
Sorry that you ended up with a broken gimbal but from the look of the video, it seems that the mavic was flying too low and the controls were a little erratic as well. At that speed even the sensors would not help you with collision prevention not because it's a blind spot but it was moving too...
I think the problem may not be the sequence of how you turn it on. It sounds like you didn't press it once and press and hold to turn on your controller. Maybe it would be good to have a read thru the user manual again just to make sure you are aware of how your mavic functions.
It's looked like is sustained a really hard fall. My heart cringed a little.
Sorry about the loss, if I were in the states, I would definitely get thunderdrones to sort it out for me