Are you sure about that? If it's the norm to pay for a share in a fleet of cars, then those cars will probably be owned and managed by a company that will ensure that they get timely preventive maintenance. Yes, there will be changes in how much is reasonable to pay for added durability, but do you have any evidence that cars need to be radically redesigned?
What's that got to do with anything? Why should driverless cars be expected to last as many years as current cars? If you're only paying for 20% of the car's lifetime cost, then you're not going to mind if it has to be replaced five times more often. In fact, you'll probably like it - that's why anybody ever leases cars.
It's quite reasonable to expect that it will be economical to pay something like 20% more for the drivetrain to make it more durable, but that's not a radical re-design.
the flip side is that if they might do better with constant use. Diesel engines for instance, do better under constant, consistent load. Engines would remain lubricated and heated. Stratification and temp changes would have less effect, etc.
