No, he didn't die, at least not that I I know about. He just popped into my mind on the commute to work a couple of days ago and it struck me how many great roles he has played.

How is this for a resume?

MASH (movie version) -- Frank Burns
The Godfather -- Tom Hagen
Apocalypse Now -- Lt. Col. Kilgore ("If I say the sea's safe for surfing it's safe for surfing!")
The Great Santini -- Lt. Col. Bull Meacham
Tender Mercies -- Mac Sledge
True Confessions -- Tom Spellacy
Lonesome Dove -- Gus McRae
The Apostle - Sonny Dewey
Crazy Heart -- Wayne

There is nothing close to a dud in that list. What I really like about him as an actor is how unshowy he is. He doesn't chew up the curtains. He sinks so deep in that a few minutes into it you are watching the character, not Robert Duvall.