Even auto makers are in big trouble because you will need far fewer taxis as they can service more people per vehicle.
The automakers are not collectively in any trouble at all, because someone is going to have to build these vehicles and that someone is going to be the automakers. Remember, there are literally billions of humans without mobility today. If these new types of transportation network permit more of them to have mobility, that represents a need for more vehicles. Some automakers will almost certainly fail, or at least some redundant marques, but there will continue to be a need for a large number of vehicles in the future. Also, for the foreseeable future, people with money aren't going to want to share their cars. And then there's also the possibility that as the car changes into something else that people don't actually drive themselves, it might actually change a lot. For example, we might wind up with a whole bunch of low-powered RVs tooling along at low speeds, with people reducing the square footage they have at home in exchange for more mobile area. No one is really sure what will happen next, which drives the economists nuts because it totally screws up all of these predictions.