Dennis said on different occasions that he wasn't gonna live long. I think the important thing to remember is what he symbolized, he was the epitome of the ultimate rock star. The greatest there ever was. With brian as the brains and carl the soul dennis was the heart.
After reading Scott's book, which deals with Denny telling Scott in the early 80s that he (Denny) is dying of liver disease, one wonders if Denny was from that point on (post medical diagnosis) very tragically hellbent on a death wish. If he really, truly felt like he was irreversibly f*cked healthwise, maybe that was further reason for him to logically legitimize not caring any longer. So, so sad. I cannot imagine the family's anguish at wondering about all the what-ifs. Simply tragic.