I think the main issue here was that the other guy was drunk. It's clear that the inebriated will have a slower reaction speed, and make bad decisions. It's unfortunate the B2M missed the cue about the other rider in a spot where he was trapped (by the fence). Sure, it might have been overly optimistic to expect reasonable decisions on the part of another rider, but we all do.

FWIW I ride on campus 'sidewalks' all the time. BTW as far as I'm concerned, if there is no motorized road to a destination, and the walkway is fairly wide then it is a road. Think MUP and you've got the right idea. When they're busy, or the visibility or other conditions are bad, I ride slowly, and when I have good visibility and few other users I ride faster (probably no more than 20 kph though).

I've worried about the face injury thing too - the mouthguard is an interesting idea. A lot of hockey players I know wear them (especially the ones with no or a 1/2 visor), and they seem to keep the teeth attached to the jaw fairly well (just look at a middle aged hockey player from the 80's now ).