I can't see this thought experiment becoming a real problem... at least not one that nations are going to work very hard to solve.
First, recognize that the road was already taken away from pedestrians with the advent of the earliest cars. Walking illegally in the street is known as jaywalking, and this is mostly a civil offense to protect people from accidents.
I don't see much changing to be honest. A determined person will step in front of an oncoming automatic car and even if it initiates the breaks, physics will run you over. There is no decision for the car to make, at a certain point. I imagine when it happens it will be handled much like regular car accidents. The person who owns the vehicle is responsible for what happens in/around the vehicle at all times.
EDIT: I'm glad I will die before automatic cars are dominant. I personally can't handle the transition. I'm too worried.
