The problem is that Uber can easily be destroyed when that happens. For example, imagine that all the German automakers decide that their fleet of autonomous cars works only for an app that they developed(maximize profits). The same can happen from the Japanese automakers, etc. Another problem is that they will need A LOT of money to buy and maintain all those autonomous cars, something that they don't do now. Personally I think Uber can die under hundreds of scenarios and survive under one or two in the long run.