The air bag is there because bashing your head on the steering wheel or dashboard is unhealthy. Not bashing your head on something hard in the first place is even better. (I'm guessing, but don't know for sure, that the front seats are sufficiently weak that they're OK to bang into.)

Back seat behind the driver is statistically the safest. In case of a collision a driver will instinctively try to save himself and therefore crash with the passenger side. Being behind the driver therefore puts you at less risk

In an autonomous ride would this still hold true?

I can't tell if thats a joke or if you're serious :)

I think they're legally required to have drivers at the moment.