When you think about it, GPS return to launch probably would not have helped here as it probably would have done the same thing.
You were just unlucky that the problem happened where it did, 2 seconds earlier or later you would have missed.
I think along the same lines as you did, altitude is your friend, and in most cases it is.
I'm actually thankful that it hit the line, otherwise it would have gone a lot further, and I probably wouldn't have found it.
At least not for a much longer time.
Only thing I can think it could have been, was the VTX cable came lose.
Just got back from flying it tonight with the gimble on.
Awesome!!!! Video to come.