Examples:
In The Gong Show, Chuck Barris announced on the first week of shows that the winners would return later to face off against each other in the playoffs. I've never seen the playoffs in all the years GSN aired the show. Granted, there may have actually been a time where did they did such a thing, but GSN may have skipped over it, presumably due to music rights.
When American Gladiators began in 1989, the winning contenders (male and female) could win $10,000 AND the possibility of returning next year as an American Gladiator. The latter was never brought up again after the first half of the first season.