Liabilty? No difference!
> “If an autonomous system acts to avoid a group of school children but then kills a single adult, did the system fail or perform well?”
This is a pretty simplistic situation as the answer is the same as it is for human driver/operators today: vehicles should not travel so fast that they cannot stop safely. If that means an AV needs to regulate its speed down to a crawl, then so be it. Since that is what a responsible human-driver would do.
And the same judgements regarding liability pertain to when someone runs out in front of a fast moving vehicle. If the act was unforeseeable then there can be no blame.
But AVs offer the possibility of having much more forensic quality information available to back up their case. Rather than "he said - she said" type disputes, there will be the ability to re-run all the recorded events leading up to an incident. There should therefore be far fewer cases of disputed liability. Though I am sure that to start with there will be many more cases of people trying to claim compo, fraudulently.