I know there are ways to measure pain, brain activity etc that most likely rule this out. But what if? Are experiences, even unpleasant ones, really experienced if they leave no trace at all, not even a memory?
So if you get surgery on your leg, it is best if you have additional anaesthesia or pain killers working in this particular leg. So you wouldn't feel all the pain even without general anaesthesia.
For an extra level of weirdness, imagine the person who caused the accident collecting the damages. It's not very improbable: you could be driving a car with your parents as passengers and you crash it, through honest incompetence, without committing a criminal offence, and they die, painfully, while you survive. Your insurance pays money into the estate for the pain your parents suffered, and you then collect that money, minus inheritance tax. By adding to your feelings of guilt, perhaps it's a fair punishment?
The world is senseless enough already. (I believe) the best we can do as humans is to try to make it a little more fair, which means connecting negative effects to negative causes. And when we do the opposite, we build systems that sow chaos. To that end, I have to say I'm actually philosophically offended by your suggestion.
If a type of accident is usually going to cause horrible pain if it causes death, this creates a bigger incentive to avoid serious injury in the first place (which also helps avoid death from those injuries).
If suffering is taken into account for injury, also taking it into account for death avoids situations where it would be preferable for the perpetrator to cause death rather than have the victim survive in pain. There's no threshold because the fatality is considered in addition to rather than instead of the suffering.