How to Dishonorable, Worst Ending in RDR2
After fighting Micah to a draw, Dutch appears and interrupts Arthur from grabbing a gun and shooting Micah. Arthur tries to plead with Dutch that Micah is actually the rat, but he sorrowfully abandons Arthur.
It’s unclear whether Dutch believes Arthur, or if he just doesn’t care. Arthur is sick and weak, and doesn’t have anything left in him. Micah grabs the gun, shoots Arthur in the face, and laughs.
The game ends with another one of the Wolf sequences that dishonorable Arthur has seen throughout the game.
That does it for how to get the best (honorable) ending, and the worst (dishonorable) ending in Red Dead Redemption 2.