The way I earn a living is the same way most musicians earn a living: By working for hire or teaching (consulting).
There are about 10,000 books that make any measurable money at all, at any given time, and only a small fraction of those earn the authors enough to live on. Even famous authors of widely read books often have a "day job."
Books I have co-authored are "pirated," mainly in markets where wages are lower than would support a local edition at local pricing. My publisher does not use DRM on e-books, and e-books still rapidly outpaced paper books.
If you do the thought experiment, lack of copyright protection or a significantly shorter term of copyright, or some other variant, like a publishers' agreement not to trespass on other publishers' author relationships for some term, would not change my direct income from book writing very much.
Publishing would adapt: Books might be serialized so that subscribers get first access on a continuing basis. Or frequent editions (which you might see anyway, with e-books) might become the norm.
Apart from the handful of authors of "blockbusters" the book publishing economy would not change that much. We have made, and are protecting at great expense a novel result: A small number of authors, musicians, motion-picture makers, etc. can make big money through mass-reproduction of their works.
Is that an advancement of civilization worth subverting all the potential for free expression the Internet provides, or not?