Duncan Long is a professional artist and writer who lives in the US. In addition to creating artwork, he has seen nearly 60 books he authored go into print, including 13 of his novels (published by HarperCollins and Avon Books).
Besides illustrating his own technical books, Long's fanciful artwork is springing up at numerous Web sites as well as on covers of novels, magazines, and CDs. An online gallery of his illustrations can be explored at: DuncanLong.com
I've traded in water color and oil painting, pen and ink; all my work is digital these days. That said, the digital medium is quite different from any others when you go beyond the mechanical, hand-to-medium interface.
I can't imagine going back to doing all my work with pen or paintbrush; it would be like going back to a manual typewriter after getting accustomed to a word processor.
It could be done, but would be a great leap backward in terms of what is produced and the time taken to produce the work.