In The Gamer's Alliance, players coming and going means their characters are often left hanging if they don't resolve their plots or put them on the bus before disappearing. This can lead to characters fading into the background never to be mentioned again although an effort is usually made to at least acknowledge in-universe what happened to the now missing characters, particularly if they played a major role in the plot beforehand.
The Massive Multi-Fandom RPG: Many players left the roleplay in mid-game; sometimes it was handwaved by having them stay in the location or die or something, but often, they just... stop appearing and none of the other characters seem to notice.
Several members of Team Snob have disappeared from Midnight Screenings over the years. The first was Jerrid, who left due to a falling out with Brad Jones (they later patched things up, but Jerrid has yet to reappear), followed by Jillian (Brad's ex-wife, who simply didn't want to do the show anymore), Jake (also a falling-out with Brad), and Violet (who only appeared for a short time in 2015, but left the show suddenly when she and Brad broke up).