Um, no.
"Origins: Beginning in January 2005, rumors circulated nationwide that Jon Heder, the 26-year-old star of the film Napoleon Dynamite, had died in tragic fashion. Some people heard he'd arrived at his final destination via an automobile accident that snapped his neck; others heard the Grim Reaper came to him in the form of a drug overdose, most commonly cocaine or crack cocaine.
We're happy to report the young man is still very much alive. Postdating the rumors of his demise was his appearance as a guest on The Tonight Show on 2 February 2005. He is currently working on two other films, Just Like Heaven and Moving McAllister. In a 21 March news article about the rumor of his death, Heder said "Yeah, and apparently it's not true."