Fan Casting Chuck Cunningham Syndrome in Sort by Tropes

Generally, if writers want to remove a character from their ensemble, they will either kill that character off or put them on a bus (or both) to explain their absence. Sufferers of Chuck Cunningham Syndrome, on the other hand, simply disappear into limbo. One day they will walk out of a scene, and just... never walk back in. They will often be retconned right out of the story's history, and everyone still left onscreen will simply carry on as if the character never existed or had any impact on the story.