The writers have finished. You’d think that they would have known who is and who isn’t coming back by now because they would have had to write them into the episode.
Well if is a scene with no dialogue, like a group pic from all cast that was there( at least the ones available), they dont need to know until close to the episode, they can take a individual pic of the actor against green/blue screen and then add it to the group pic with for example a SB background, in that case no need to even write dialogue for it.
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"I offended you with my opinion? Ha, you should hear the ones I keep to myself".