I realize you are just trying to be helpful but really, your friend ran into a fence, not like a sudden moving object. It seems like that isn't really an issue of having a brake or not but going too fast without a brake.

I've ridden both with a brake and without and my only accident came when I went over the bars by slamming on my front brake on a downhill. Not sure it was more helpful than a powerful skid would have been but since it was there, I hit it.

Everyone knows the risks and people have accidents, both with brakes and without.

Best wishes for a speedy recovery to your friend. Crashing suck no matter what the circumstances.