I can appreciate the story. And I see that your association with the driver shaped the way you feel, and I can respect that. In fact, I've basically told my family something quite similar, that in the event of an accident, aviation or otherwise, don't go out for blood if I don't make it. Unless there is clear negligence, don't let anger, and resentment against the other culpable person rule your, or their future.
Now, having said that, we need to address two other things that I think are cogent. First, law is not based on emotion in a republic. We are not an eye for an eye, or a vengeful society(in theory, we all know it happens). We use the law to determine responsibility, and the mitigation factors are only in play, after a determination of guilt or innocence is completed, at which time the guilty party may have a very wide range of punishment accorded. So - when I read this story, your friend had a hard go of it from the time he was 17, until many years later. He suffered, and sweated, and hurt for years. But - his suffering was by your own admission, a result of his own actions. Maybe he was reckless, maybe it was a deer, but the fact that he agreed to a license suspension tells me that there were enough mitigating circumstance that the law felt he was culpable for being somewhat negligent. This is what I was talking about previously. Even if it was a deer which was the proximate cause, his driving style clearly contributed to the damage done.
Now, speaking about the damage done. On the one hand, we have an injured young man, with years of pain, and rehab in front of him. Permanently damaged, by his actions behind the wheel and that surely is sad. On the other side - we have a grieving family, who has lost the life of their offspring, and maybe brother, sister, cousin for ever. He's never, ever coming back, and will never comfort his family again. This is sobering enough, and the damage done, can't be ameliorated by years of rehab.
I don't know any more than I've read, but in this case - I have to side with the law. They took away his license, and after the years he spent to get it back, finally I'm pretty sure he never ever would drive with abandon again. So - the philosophy of punishment and rehabilitation(criminal) seems to have worked perfectly in this case.