Copy writers' skill is always in very high demand.
If you think that advertising is the only industry where copywriters find employment, the you are wrong.
Look at some of the other fields where copywriting skill is needed:
Sales pages for ebooks, and software
Film industry advertising
Brochures and flyers for all kinds of businesses
While some people are natural copywriters, other, who genuinely aspire to become high paid copywriters learn the tricks through various books written by legendary copywriters.
Here is an ebook that I recently came across titled, "Copywriters Blueprint"-a complete guide copywriting.
If you would like to learn the deepest, darkest secrets to the Internet's most sought after copywriters who have generated thousands of dollars for every single page they write, then you should read this Copywriters Blueprint.