I had a similar response, charcoal is still used to draw with and that is what, 100,000 years old by now?

The interesting challenge will be that there is a certain level of industry required to support the manufacture of base film stock, and making the chemicals to develop it. As the number of users goes down, the base cost of that development is spread across fewer users (higher per user cost) and at some point nobody is will willing to pay the full cost of supporting the industry. It is, by definition, the equivalent of the power curve in flight, higher prices lead to fewer users, which leads to higher prices, until you are down to 1 user paying for all the costs. Sometimes you can recover if new manufactures can come in at a lower level but without that you lose the ability to support many ways in which film was used.