Just out of curiosity what quick release knot would you suggest, i know about 30 knots and none of them would have helped in this situation.
I only know two but I guess the critical thing is not the knot but being able to get to the knot, isn't it. So it's a trade off between the risk of your untethered dog jumping off the boat and the risk of not being able to get to the knot if the boat capsizes. Got to choose between them I suppose. Or there's the 'no fun' option which would be to not have the dog on the boat.
I guess it's the speed at which the crisis happens. You'll never reach the end of rope before incident. I prefer my dog can escape free and fend for himself in case the unspeakable happens. I am a kayak guide, a level three canoeists, Yachtmaster, ex- ski patroller and commercial licenced Maritime officer and a volunteer fire fighter. I prefer he can escape independently of me having to sever a line. Perhaps the best option is to attach him using a HRU ( hydrostatic release unit) they are what attach the liferaft to the boat. They automatically release at about 1.5 meters.