My 800 quad took a nasty tumble and I would appreciate help with the log. Although it’s hard to tell because of the damage, I think one of the motor tubes pulled enough to allow the motor to turn and I think the logs confirm that possibility. I’d really appreciate it if someone with more experience interpreting these would have a look. It was a short flight and the crash is at the end.
good description, and from what I see it’s most likely correct.
You certainly had some machanical failure, it’s clear from around line ~11080 when plotting Roll/DesRoll.
Usually, if thrust on one arm failed, we’d see a RCOUT.Chan go to max, when trying that arm up.
Instead - you can see chan1 go very low , as it’s trying to control yaw.
Depending on which way the motor assembly would rotate on the arm, this looks correct - we could of course find that out by analyzing the RCOUT actions, but that’s too much work. 
your conclusion is correct.
Yes, you had a mechanical or electrical failure on a powerplant.
I wouldn’t set THR_MIN that much higher than default unless necessary to keep the motors spinning. Your vibrations are ok but not as good as a typical 3dr copter with pixhawk mounted on its foam. Your compass performance is adequate.