I understand that he was infamous for his erratic behavior and drunken antics, and had trouble finding people who wanted to perform with him for the last couple of years of his life…
Sad, as everyone seems to agree about how very talented he was when he was at the top of his game.
He was obviously just a frustrated, temperamental artist, due mainly because he sucked.
Has Christopher Reeve been mentioned yet? I think he would count even if it did take him a very long time to die.
Yep, I wish she would have stayed around a little longer. 
Hemingway committed suicide in his 60s. He was probably good for another book or two.
It wasn’t his being at the height of his success that killed him. It was the lack of height! 
Jimmie Rodgers, the “Father of Country Music” was struck down in his prime by tuberculosis.
Humorist Will Rogers perished at his peak in a plane crash.
He was definitely on the way down, I’ll agree with that.
D. Boone of the Minutemen. Killed by a drunk driver after IIRC Double Nickels on the Dime came out.
I almost feel silly mentioning this one.
Since nobody brought him up before now I gotta think there’s a reason, but I’d put Douglas Adams on this list. Yes, you can argue that HHG was his masterpiece but he himself was never satisfied with the final book and there were rumors that he was penning yet another addition. And The Salmon of Doubt, a new Dirk Gently book, was masterfully underway at the time of his passing. Somehow I don’t think he’d hit his peak just yet.
I was going to put in another vote for Nick Drake, but he actually had three years’ mental decline between releasing the haunting Pink Moon, and his death in 1974.
What about Natasha Richardson?
Seems to me she was doing pretty well for herself when she died.
… and Esbjorn Svensson. We miss you Esbjorn.
Possibly. Toure was producing some of his best work when he died, however.
Federico García Lorca.
Marilyn Monroe, anyone?
Divine. After decades of cult status, he was on the verge of breaking into mainstream stardom with “Hairspray”. He died one week after the film’s release.
She’d been in decline for the last couple of years of her life, her last finished movie, The Misfits, was not a success (and she was apparently in horrible shape and behavior during its filming.
Dinah Washington is arguably similar - no doubt she died too young, but she was at least two years removed from her biggest successes. Not quite the very height of her success.
If Jonathan Larson could have held on a few weeks, he might have qualified…
Oh, dear lord. Did I forget Bill Hicks? Greatest comedian ever.
Speaking of comedians, Mitch Hedberg.
It could be argued that Buddy Holly was past his peek when he died.
Not at all; Buddy was just beginning to peak. He was only in the music biz, in the technical sense, for less than 2 years and became one of the most influential artists ever. Had he not gotten his ticket punched at just 23, he would’ve been bigger than Elvis.