To answer your first question: In my opinion, no one knows truthfully if authors will always be able to make money off writing books. I would say probably so. You can look at history and trends. Books have been around a long time, even with the invention of new technology (radio, film, television, talking books, board games, entertainment venues, cable TV, videos, VCRs, video games, computers and software, desktops/laptops/tablets..., cell phones, iPads). Many authors are busy writing books about the new technology. And more people have become writers (Think blogs, forums, texting, etc.). Creativity has little to do with why some people write. Demand is the engine which drives the writing machine. Everything must include instructions on how to operate it. Then, there's the competition and the need to improve upon existing technology/books.
In answer to your second question: The environment and world events will dictate the population size, their access to reading materials, and their ability to read. If anything, people have to read more to stay informed about new and emerging technology, not to mention college and the job market. I think there are lots of people reading, but fewer may be reading for pleasure, because they have to read more for educational and informational reasons.
Think about on-line classes, on-line books, and ebooks. A degree can be earned completely online from almost anywhere in the free world. On-line books can only be read while online, while ebooks can be downloaded and read anytime on an ebook reader, like the Kindle, without worrying about floor storage. There is little or no interaction with multi-media. Access to a computer, iPad or Kindle or iPhone is needed with both on-line books and ebooks. When people need written information fast, this is how they get it.
Paper books are portable and can be taken most anywhere anytime. They can be loaned, borrowed, or bought. I don't see any libraries closing around here. If anything, they have increased their resources to meet the demand for both paper and on-line readers. There are digital libraries, like Cambridge University Digital Library..
Online books - Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Online_books