|Saturday Night Live (Oct. 11, 1975) [Immigrant]: Dies of a heart attack when he repeats Michael O'Donoghue's actions after Michael has a heart attack. (It's likely that he's not actually having a heart attack but only imitating Michael's reaction, but since it's been suggested, I'll list it just in case.) (Thanks to Tommy)
Saturday Night Live (Oct. 25, 1975) [Square Dancer]: Shot to death, along with all the other dancers, after the dance caller (Dan Aykroyd) instructs them to shoot each other.
Saturday Night Live (Jan. 10, 1976) [Don Vito Corleone]: Dies of a heart attack during a group therapy session. (A parody of Marlon Brando's death scene in The Godfather.)
Saturday Night Live (Jan. 31, 1976) [Duke]: Accidentally shot in the chest with a rifle by Chevy Chase when John comes downstairs, as Jane Curtin looks on in shock.
Saturday Night Live (Apr. 17, 1976) [First Violinist]: Appears as a corpse, propped up on stage as part of the "Dead String Quartet."
Saturday Night Live (May 15, 1976) [Bank Robber #1]: Shot to death in a shoot-out with police.
Saturday Night Live (July 31, 1976) [Cooperative Man]: Shot repeatedly in the chest by Dan Aykroyd and Chevy Chase after John opens the door and agrees to answer their questions.
Police Squad!: Testimony of Evil (Dead Men Don't Laugh) (1982; scene deleted) [Special Guest Star]: Drowned after having his feet encased in cement and being dropped into the water. (Due to John's real-life death, this scene was cut before the episode was broadcast, and replaced with a different scene featuring William Conrad. The footage of John's scene is now believed to be lost.) (Thanks to Tommy)
Blues Brothers 2000 (1998) ['Joliet' Jake Blues]: John does not appear in this film (as it was made many years after his real-life death), but it's established that his character from the original The Blues Brothers (1980) had died at some point between the two films. (Thanks to Tommy)