As for being a flight instructor, that doesn't confer any special set of skills on the pilot. No more than does being an orthopedic surgeon protect one from blunt impact trauma.
Very sad story.
MU-2’s have an accident rate 2.5 times others in it’s class, for a variety of reasons, but almost all come down to PILOT TRAINING.
I lost a friend in one of these years back, and SD Gov George Mickelson died in one.
That said, they are about the most efficient aircraft in it’s class, and, I’m told, a joy to fly. (just don’t forget to watch the sink rate).