Ozzy Osbourne is still alive, at 74. He was as much of an alcoholic as MacGowan ever was, if not worse (although I don't think Ozzy ever did heroin?)

Dick van Dyke is still around at 97(!) in spite of many years of chain-smoking and alcoholism (he stopped drinking in his late 40s, and smoking in his 70s). Look, I like Dick van Dyke and I wish him many more years, but he ought to have died decades ago.

Biology is funny business.