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 did not reappear until 2016), 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 while Brad was dating her, but she left the show suddenly when she and Brad broke up). Lesser secondary reviewers, such as Brad's mother, Leslie, often tend to go several years without appearing.
The absence of Dick Masterson, co-host of the popular podcast The Biggest Problem in the Universe, was not mentioned at all in its abruptly released series finale, due to a falling out with his co-host Maddox over an ex-girlfriend that has since escalated into a public feud.
Supermarioglitchy4s Super Mario 64 Bloopers had several real-life Youtubers, known as the YouTube Rangers, as recurring characters represented as Mario recolours. However, since SMG4's falling out with them years ago, most of them have completely vanished from the series.