We can only assume of prescription painkiller overdose or the like.
http://www.nytimes.com/2013/10/03/books/tom-clancy-best-selling-novelist-of-military-thrillers-dies-at-66.html
Tom Clancy, whose complex, adrenaline-fueled military novels made him one of the world’s best-selling and best-known authors, died on Tuesday in a hospital in Baltimore. He was 66.
Man, I love a good terrible, terrible, terrible author's death. This is slightly more exciting than when Robert Jordan (aka Jimmy Ringley) died, and obviously a pale shadow of the global celebration by people who can read that will follow Dan Brown's inevitable death by falling illuminanti sculpture.