We may be asking the wrong question. It's not about how many die on the bike or in the car. What about health benefits? I believe every time you get on a bike instead of in a car you increase the odds of experiencing quality life (independent of injury risk):
1. The health benefit will increase your lifespan and the quality of those years
2. It is just so much more darn fun to be travelling on a bike than in a car.

Of course #2 will only happen if we feel safe on the bike and that has a lot to do with how many people die on a bike or in a car, or how many of each we know personally. I personally know 5 people who have died in separate car accidents, all of them tragically young...9 yrs old...13...18...19...21.