Future episodes become inundated with references to the Olympic Games.
Related to the above, Michael Phelps appears in a future episode.
And the song done by David Armand for "Face the Music" is "Harder, Better, Faster, Stronger".Other guests that may come back thanks to Whose Line involvement:
Richard Simmons, Stephen Colbert, Whoopi Goldberg, Kathy Griffin. Before he died, Sid Caesar could have probably ended up doing a two-parter thanks to the sheer number of tales he had, including that time he punched a horse. Really.