Yeah, making an Uber-or-Lyft-like service is easy. Lots of people have done it. Uber and Lyft price-competed those services into irrelevance, but if another service has self-driving cars and Uber-or-Lyft don't, then they won't be able to price-compete effectively.
I think it's likely that if Uber-or-Lyft don't get a sustainable technological advantage with driverless cars, they will actually stick around and make a deal with the company that provides the driverless cars, but they will have a weak negotiating position and will have to accept a small percentage of the profit which will not justify their current valuations (especially Uber, which has a much higher valuation than Lyft).
I think it's likely that if Uber-or-Lyft don't get a sustainable technological advantage with driverless cars, they will actually stick around and make a deal with the company that provides the driverless cars, but they will have a weak negotiating position and will have to accept a small percentage of the profit which will not justify their current valuations (especially Uber, which has a much higher valuation than Lyft).