The more I read about this, the more amazed I am. The claim is they were negligent in not ballasting the tractor, but it had a box blade. If they had insisted he buy the ballast box, it would have been taken off to put on the box blade, and the box blade probably weighs as much as the recommended ballast. If you can roll a tractor 1-1/4 times with a loader and box blade attached, I doubt that loaded tires would have eliminated the problem.
The only way I can see that this tragedy could have been avoided would have been a seat belt interlock and non-foldable ROPS. It's probably only a matter of time.