I like the suicide theory, but I notice that kind of death is really not very common on soaps. The real badasses are murdered, but David is actually pretty likeable. His character is written very well, really - he's two different men, one with Nikki and one while he's gambling. An interesting depiction of addiction, and more realistic than the rich women alcoholics (Kay and Nikki) that we've seen previously.
I see Paul playing a big part in David's demise, whether he dies, goes to prison, or possibly just runs off and is never heard from again. Until the writers need him, of course.