Really sad news.
As a lousy swimmer, you won't catch me putting myself in positions of great risk. No bungy jumping or mountain climbing for me, so ergo no russian roulette with fast rushing water. I just don't fish those areas of the cap...
That being said, I don't believe in any closures. They can post signs, give warnings, etc, but the rest is up to the individual.
Closing it down would be like closing down everest for climbing because too many people have died. You just need to remind them of the risk level ( a few laminated newspaper clippings on the trail would help), and let them decide what level of risk they want to take.
I like the idea of clipping on a safety line.. If I'm fishing that stretch I would probably do that, combine some mountain climbing gear with fishing.. You don't need to go to the extent of a cable line to clip on, just a tree or boulders would be better than nothing.
Everyone stay safe this year... remember it's a hobby, no danger pay.