Has an AFL game ever ended 79-20?
Exactly once. On July 27, 1901, Essendon beat Carlton 79-20, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 79-20 in league history.
That makes 79-20 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 80-20 has happened never and 79-21 has happened never.