If he can make 12 years' worth of Rex Morgan MD jokes funny, he can probably write a pretty good novel.
Josh Fruhlinger, whose blog The Comics Curmudgeon is one of the few things I regularly read on the Internet, wrote a book called The Enthusiast a while back. I haven't read it yet, but it's on my list to get.
He wrote a very informative and interesting article about how much he made and how he did it. If you're a would-be or struggling writer, it's worth reading. Check it out here.