What's preventing Uber customers to gather a few phone number of Uber drivers, and if Uber dies, to message them directly for a ride? It's a bit of a hassle, admittedly, but if you can contact the providers directly...
How many drivers' numbers will I collect? I need the app to contact the nearest driver. Also, the pool service is highly difficult to recreate without the infrastructure uber provides. You'd basically have to start another uber.
The fact that Uber facilitates payment, for one, and that's handled external and prior to the ride, so you don't have to worry about the hassle at the end. Also the infrastructure around tracking who needs a ride and where they are is nice.