Yeah, I don't really understand how any company will be able to maintain a fleet of driverless vehicles. Uber works because you download costs to the driver.
That's a common misunderstanding.
Uber pays what the drivers are collectively asking their rates to be, and the rate is established on the average driver's needs, that encompasses not only car ownership costs, but ANY costs, even food, housing, health care, education.
The car ownership costs can vary per driver based on various factor that influence how much of a ROI the driver can generate through Uber and other means with his car (bringing the kids to school, going to work, whatever, doesn't have to be something that pays).
Uber doesn't just throw some pocket change out there, it throws what it needs to provide to have drivers willing to participate and that's a result of costs associated with every aspect of the driver's life. Renting isn't "passing the costs to the owner", and Uber is renting their fleet and employees, so costs could be optimized if they didn't rent.
If the driver's own costs were to go down (remember that is related to all of the driver's expenses, not just the car's), Uber would be able to pay them less accordingly, and if those costs instead rose Uber would have to pay more. If rents rise in a city, Uber has to pay more. If rents go down, they can pay less.
So now you take that into account and ask yourself if Uber wasn't renting, and didn't have to pay for a driver at all, could their ROI be higher? I think historically you can argue that yes, their ROI would be higher.
Right now Uber pays every time a driver is hungry, needs new clothes, needs to make a payment on his mortgage, etc. One way or another, a part of those costs are transferred to them.
If they get rid of the drivers, they'll either just still rent the self-driven cars, in which case they continue to pay for the costs associated with the cars as they did before (production, maintenance, insurance costs which would be lower anyway, etc.), cars that may well not be rented 24/7 as different companies could rent them for different needs at any time depending on availability and demand, but they don't pay for any costs associated with the drivers themselves anymore.
It's pretty much absolutely certain that at the end of the day, the ROI is much higher if the cars are self-driven. The cars end up being used almost continuously, so the usage rate is very high which is something that is economically favorable, whether by Uber or Uber and other companies, and costs are kept to a minimum.
This is pretty much true for any job that requires people, and it's why it's often counterproductive for companies to be against social safety nets since a well implemented one actually reduces employee costs for employers, as employees are less demanding regarding their salaries if their own costs are lower.