A legal question about Roman à clef

Asking this question because I've been toying with writing a very loose roman à clef, and am interested in the libel issues surrounding such novels.

I have an idea for a novel that sprang from thinking about the sharp downward spiral in the career of a certain internationally-renowned cultural figure, and wondering just what might have caused such a precipitous fall in their creative output... Anyway, from such idle thoughts I've pieced together a story about a creative type with a similar career arc as the real-life subject, and who shares a few biographical details with the real-life subject; the plot to explain his artistic down-turn, however, is entirely fictional and of my own devising, and to all intents and purposes my 'hero' is a completely different character, in personality and deed, to his 'inspiration'. Really, all I'm using for the novel is the artist's career arc and the cultural context they were working in (while creating my own characters to stand in for the 'hero''s creative contemporaries), as a spring-board for the story I want to tell.

My question is, will this still get me sued to buggery? Obviously all such issues are questions of degree, but how have other authors who've penned roman à clef managed to escape the legal ire of their inspirations? I know its crazy early to worry about such things, but I've been thinking about it lately and have to admit I don't really know how the land lays. Do all authors of roman à clef run the risk of legal action? (This question is also in-part inspired by reading American Tabloid recently on holiday, and wondering how Ellroy could get away with writing such salacious stuff about real-life characters, much of which is unconfirmed and fodder for rumours and gossip)

ps I'm not seeking to specifically satirise or lampoon the artist in question - indeed, I'm aiming to humanise my 'hero' more than make him a target for scorn or laughter - but the career arc will be pretty much instantly recognisable as that of my 'inspiration'.

you'll be hearing from my lawyers

michael jackson is dead, which changes some things legally

and indeed, medically for that matter

Never really understood how this was qualitativly any different from RP Fan Fiction.

Yeahp, you can't defame the dead, which is why James Ellroy could get away with the stuff in American Tabloid (and why he won't be continuing with his Underworld USA arc into the Reagan era - too many people still alive).