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I think that would generally fall under Put on a Bus (The Bus Came Back when they return). May also be Written-In Absence, which is generally when the actor needs to be absent for whatever reason, so the writers make up a quick excuse. If it's medical, could be a Convenient Coma. If the reason the character is removed from the plot is because they're the one capable of solving everything in five minutes, it involves Deus Exit Machina. There's also Absentee Actor, when the character isn't there and no one even bothers to mention it.
Are there any tropes that involve getting rid of a character temporarily from a story until their presence is needed? For example: They are present at the beginning of the story, something happens towards the beginning of the 2nd act (called away somewhere and/or injured) where that character ends up absent during a good chunk of the story, and then they return towards the end. Does anyone have any good examples? The medium doesn't have to just be film.