It's a legitimate question but the mechanism of how it works is completely wrong. Many people will be killed by any given mass market implementation of self driving cars. Those people will be killed by crashes that a human could not have avoided, people will be killed by errors few humans would make (e.g. "plowing into an overturned truck at full speed") and people will NOT be killed by facets of the system that humans cannot replicate (never tired, never drunk, never angry).
Dozens, hundreds, or even thousands of people will die between "bug fixes". The only metric needed here is to determine if the system as a whole performed better or worse than a fleet of typical people. We know what the accident rate is for a fleet of typical people (for now) and it is pretty bad. People also occasionally drive into obvious trucks for no known reason. People are inattentive. People are emotional. People rush. People ignore things they shouldn't or react too late to things they should. The bar to operate more safely than people is high, but not impossibly high.
In response to market changes, world changes, and continued investment, code will change but also input training samples will change, labeling technology will change. Those changes will result in a measured change in the fleet's performance.
There will be cases where a single death results in some code change. Early on there will be many such cases. But as time goes on, those cases will become less and less frequent, as the cases where specific code points are needed become not only unnecessary but even an impediment to the proper mapping of world features to behavior output.