Being able to punish someone doesn't change the fact that a crash happened and it doesn't change the fact that someone died. There is a difference between punishment and justice, there is rarely ever perfect justice in life.
The best we can do is mitigate harms as much as possible, and it seems self-driving might be the best mitigation of traffic accidents compared to human drivers.
But in 5 years if there are multiple self-driving offerings competing on things like price, door-to-door time, OPEX (e.g. does a camera-only system with no moving parts need less skilled maintenance?), then someone may try to be the cheap but good enough self-driving service that cuts corners -- and we should want some execs to actually go to prison rather than just some cost-of-doing-business fines.
* 2 deaths per 100,000 per year, but no one goes to jail
Because apparently going to jail is important for some reason?
Honestly, choosing jail is somewhat dystopian IMO