This is the exact reason why we need Nationwide disclosures of automous miles driven. California requires this stat, so it's data is the most telling.

California .92 deaths per 100 million (human)vehicle miles traveled. There were only 500k autonomous miles driven in California last year.

I'd bet your guess about death rate per mile is right considering waymo which has largest and most advanced fleet only drove 2 million miles nationwide last year.