It will take decades before the autonomous fleet takes hold; during that time there will be advancements in medicine that fills the gap (like 3D printed or grown organs). Taking parts out of one meat bag into another will seem primitive.
I thought you were going to point out that even if we cut the death-by-crash by 2 or even 10, there will still be many deaths in autonomous cars. That will take some getting used to! I hope as more cars are autonomous we'll see a drastic reduction due to the network effect (if 1 out of 5 cars is driving safely, the other 4 might "join in" by proximity).