Insofar as there's an ossified idea of what a novel is, you're probably right, it may become obsolete. On the other hand, insofar as "novel" literally means "new," there will always be something new, because many people have an urge to create. I think you're right that there's increasing demand for shorter work. Which doesn't necessarily mean that that's what the artist wants to create, but it's pressure we feel. I write a lot on Medium because I'm compensated a few dollars for a relatively short essay. I have books for sale, but no one buys them.