Sad news indeed, especially if the incident was attributable to incorrectly fitted Q/R wheel and could so easily have been avoided.
Sometime before my 2016 car was built one of the three steering wheel attachments was fitted by the factory with a longer bolt to limit movement of the spring loaded removal collar. Many, including myself replaced this with shorter to allow quick removal. There are two sets of splines the wheel needs to fit over when re-attaching. It is possible to fit it located on just one although the excess movement is fairly obvious.
I've experienced the wheel "1/2 on" issue, although fortunately only when backing out of the garage. It's unsettling to say the least... I recall being surprised that the Q/R adapter allowed this half-way condition. Have not looked closely at the design, but I would think all or nothing condition would be better with respect to re-fitting the wheel...
When I picked up my M3W, the dealer shared a story of a customer who had the situation while driving on a highway, by way of a warning to me to ensure it was fully seated. Thankfully, that situation didn't result in an accident, but easily could have.
