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.
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.
Early stories in Metamor Keep often featured Magus, the most powerful wizard in the Keep. The problem was, Magus was based on a real person, who became increasingly uncomfortable with being used in an increasingly complex and dramatic story. A Canon Foreigner wizard named Wessex was introduced, but Magus continued to be used until the universe controller put a ban on using him. In-universe, however, he simply disappears with no explanation.
Several members of Team Snob have disappeared from Midnight Screenings over the years. The first was Jerrid Foiles, who left due to a falling out with Brad Jones (they later patched things up, but Jerrid has only made cameos since), followed by Jillian Zurawski (Brad's ex-wife, who simply didn't want to do the show anymore), Jake Norvell (also a falling-out with Brad), Violet Rinorea (Brad's next girlfriend, who left when the two broke up), and Brian Lewis (who left all of Brad's shows amicably). Lesser secondary reviewers, such as Brad's mother, Leslie, often tend to go several years without appearing.
The earlier episodes of Queer Duck showed Queer Duck to have a straight brother named Lucky and a nephew named Little Lucky, both of whom were eventually phased out and never acknowledged again. A flashback of Queer Duck's hatching in the short "Quack Doc" indicated that Queer Duck was the Ducksteins' only son, plus the short "Homo for the Holidays" introduced Queer Duck's lesbian sister Melissa and had Queer Duck's boyfriend Openly Gator remark that he didn't know Queer Duck had a brother, indicating that Melissa was Queer Duck's only sibling.
SMG4's Mario 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.
The "what aged worse" segment from Gilmore Ball Z is absent after a few episodes