It depends, if the bus is empty or full of kids. This is just one example... I doubt there will ever be enough information to program for all circumstances . It will be more like if something happens shutdown and wait for human instruction on how to proceed. Wouldn't there be a network in which the robotic cars could warn others in time to avoid having to make such choice in the first place?
Also, I do not think it will be the gap between how safely an automated vehicle drives as compared to a human counterpart that will stop humans from driving. I think humans will stop driving so it would allow for automated vehicles to drive safely, since there will be less data to take into consideration if all the vehicles are using the same exact operational procedures.
We should automate vehicles to take over the mundane tasks of driving the vehicle and leave the decision making to the human operator. We are the highest order of intelligence for making such decisions (thus far).