Not knowing the details of the accident it would be difficult to give an objective opinion. Based on a minimal set of facts, my opinion is that it does not matter if the bike was geared or not; I doubt your friend would not have changed gear before going on the road and: People need to to be accountable for their own actions. Accidents do happen.
I taught CBT as a volunteer instructor for many years. I was not paid for it and did my best to make sure people were ready to go on the road. All you can do is judge the riders ability prior to road riding. Once out on the road it is down to the rider to ride safely. An instructor will often put themselves in vulnerable positions to "protect" the learner but can not control their bike. There are loads of people riding around today with a CDT certificate signed by me. Without instructors there would be no one learning to ride.
Sorry about your friends major accident but there are too many "no win no fee" people in the world today that cost the rest of us money.