Great point, however if these autonomous vehicles are electric (and I'm not saying they would be), they'd require much, much less maintenance than a fossil-fuel based autonomous fleet.
If you are running a fleet of cars or ride sharing yours all day when you are at work, its going to get 100k miles put on it a year. Expect a new battery ($5k-$10k) annual replacement, in addition to the other 80% of the car that isn't hybrid like suspension, electrical system, interior and body.
The fuel savings often goes into battery maint/replacement, if you plan on keeping the car for extended mileage/time.