The function of characters in a scene is not to establish their physical presence, but to represent their points of view on the topic at hand. As long as they fulfill that mandate and throw their two-cents into the mix, their actual presence is not required.
As authors, how can we represent a character’s point of view in a scene without having to haul him in and place him there? Perhaps the easiest way is to have other characters talk about the missing character and relate the opinion that character would have expressed if he had been present. For example, one character might say, “You know, if Charlie were here he’d be pissed as hell about this!” The conversation might continue with another character taking a contrary position on what old Charlie’s reaction might be until the two have argued the point to some conclusion much as if Charlie had been there in spirit.
Other techniques might use an answering machine message, a letter, diary or video interview from the character in question that is examined in the course of a scene. Many current stories use a murder victim’s videotaped will to include him in scenes involving his money-grubbing heirs. More subtle but potentially even more effective is for one character to examine the apartment, studio, or other habitat of a missing character and draw conclusions based on the personality expressed in the furnishings and artifacts there. Even the lingering effect of processes a character started before he left, or other characters’ memories of the missing character can position him in the midst of intense dramatic interchanges without his actual attendance.
From the Dramatica Theory Book