I believe that if they wanted to leave, they can, and it will not hurt their bottom line. Now, it's highly likely that drivers will get screwed, but how bad, we'll just have to wait and see.
Now, remember - Uber, is a Technology Company. That is why they are able to circumnavigate a lot of laws that were put in place to protect the average worker. And for the government to come in and say you guys will have to collect sales tax and have them treat it like a brick and mortar store is a very slippery slope. In other words think of it as collecting tax from the internet.
Sales taxes fund government, projects, and protections for workers, but it will not apply to an Uber driver because he/she works for a Technology Company and is not afforded the same laws and regulations. Yet, we'll be required to collect it, if it passes.