Note that Tesla owns the super charging stations, and is also aiming to stand up a large scale battery production facility. Assuming that the patents would lead to other auto-manufacturers to use the same standards that Tesla uses, this would mean that the would need to either build their own batteries, or buy them from Tesla. Since Tesla is making the Gigafactory so that the price of batteries will drop, it's likely to be cheaper to buy them from Tesla than standing up their own infrastructure to handle it. So, even if they aren't selling as many cars as the big automakers, they can still sell batteries and access to the super charging stations to the big players.
In any case, I think a sufficient amount of people would probably still buy a Tesla because of the brand recognition, even if the big auto-makers were making solid electric cars.
In any case, I think a sufficient amount of people would probably still buy a Tesla because of the brand recognition, even if the big auto-makers were making solid electric cars.