Harness has saved my bacon before. Also in that incident, I would have been screwed without the string (tether) tying the top of a climbing stand to the bottom part, as the bottom part was left hanging when the cotter pin came out: So, to summarize, these are important/imperative:
1. Use a harness, use a harness, use a harness - always, with a climbing or strap-on stand. And obviously, use the harness on the way up and the way down as well - not just when you're up in the stand. The time most prone to falling is moving up or down, or getting into out out of the stand, in the case of a strap-on stand. Once you get above 5-6 feet off the ground, the harness needs to be around the tree.
2. With a climber, tie top to bottom.
3. Carry a spare cotter pin (of course, with a locking mechanism of some sort) in your fanny pack or pocket (I didn't have a spare, but I made my field repair by substituting a little screw-in tree gear hanger hook as my "cotter pin" for securing the cable on the bottom of the climbing stand, to get down).
4. Carry a cell phone on you if you have a signal at all where you hunt.
5. Wouldn't hurt to carry a whistle too, preferably around your neck.
6. Let your buddies know at least approximately where you are going to be hunting with your climber (and when).
7. Carry a knife so that you can cut yourself out of the harness if necessary. Falling to the ground and risking injury that way is better than hanging there freezing to death. Knife needs to be accessible, so something like a kneck knife or sheathed belt fixed blade is preferred.
8. If you're clumsy and/or out of shape, you might want to just use a blind and forget about the tree stand. Safety first.
9. Replace all nylon straps at LEAST every 2 years (every other year), but if you have a lot of wind and rain, then every year is preferable.
As tragic as it is, if you could get your parapalegic victim acquaintance on video to present to the kids, that would help drive the point home a lot - something like a recorded video statement if possible. If not, then a picture of him in his wheelchair along with a written statement from him would help. May his suffering help others avoid suffering.