We punish people for speeding, driving under the influence, or texting while driving because those behaviors are reckless and we want to deter them. That makes sense.
But what about a freak accident where the driver did nothing wrong? Should they still be punished just because it happened to be them in the wrong place at the wrong time? In my opinion, no. If they didn't do anything reckless or negligent, there's no reason to think punishment would teach them anything useful. At that point it just feels like we're satisfying our need for vengeance rather than serving any logical purpose.
With a self-driving car, every accident would basically fall into that "freak accident" category. The car wasn't distracted, drunk, or driving recklessly. Maybe you could argue the company should pay compensation to the victim's family or at least cover medical costs if the person survived as a gesture of good will - but I don't see how the company would be morally responsible in a way that justifies fining or punishing them.
Just thinking aloud here. I don't know what the actual answer is.