To put this accident in perspective, Uber self-driving cars totaled about 2 to 3 millions miles, while the fatality rate on US roads is approximately 1.18 deaths per 100 millions miles [1].
At some point, autonomous vehicles will be carrying cargo instead of passengers. When that happens, fatalities per mile driven will no longer be a valid comparison between manned and unmanned vehicles, as catastrophic accidents will have fewer people involved.
I do think it'll always be fair to consider total lives lost per usage metric, regardless of if people were in the vehicle or not. The lives of drivers & passengers have equal value to the lives of pedestrians.
This Rand study looks at impact of lives saved and recommends that "Results Suggest That More Lives Will Be Saved the Sooner HAVs Are Deployed". Any mishap, while most unfortunate and tragic for everyone concerned, should not result in kneejerk reactions!
Statistically, I don't think that miles driven on lonely freeways equal those in Manhatten. And perceptually, running down city pedestrians at 40 MPH will impact public thinking more than highway fatalities.
It's impossible to know. The simulation needs to be very good with thousands and thousands of all the weird situations that can occur in the real world. Without knowing how sofisticated the simulation is and if they also are using generative algorithms to try to break the autonomous system you can't even ballpark it.
[1] https://www.nhtsa.gov/press-releases/usdot-releases-2016-fat...