1) Overall miles will go up - yes I agree - but I do not think this it obvious but counterintuitive. Obvious for us because this has been brought up several times over more than a year and we have red pilled on it.
Also once one accepts miles driven will go up then comes the second surprise they will go up a LOT...more people going more miles...and then with communting farther because of real estate and lifestyle arbitrage and the ability to work during transport miles driven goes to a level beyond a LOT...
2) Personal vehicles will remain essential especially in sparsely populated areas. The more densely populated the living area the easier it will be to rely on autonomous fleets. It is already the case if you live in the densest areas in cities like New York or San Francisco or Boston you can live without a car. To drive away for the weekend there are short-term rentals. Parking is expensive. Autonomous fleets will be efficient in the suburbs or dense areas wtih single family homes as well. But in these areas you might find mixed use of private cars and autnomous fleets.