...However, if you choose to kill him right there and then, it turns out you're stabbing an illusion. Also, the Emperor completely forgets about that incident straight away, and will proposition you regardless.
Except that this never became part of *my* playthrough, because I did not ?
I agree that it would be nice if there were a different case for the Illithid romance if you decided to stab them.
Though the Emperor just using sex as manipulation tool would be fitting, too. After all it is clearly stated before the encounter that you can only trust an Illithid when your goals are perfectly aligned, so you are only interesting when you decide to turn Illithid yourself and align your goals. Though this information is unreliable as all information in the game. Later they clearly state that illusions are its nature.
Except that the Emperor might actually be a case of a rogue Illithid who recovered some bonds — emotional or otherwise. There are cases of rogue Illithid in D&D lore:
https://forgottenrealms.fandom.com/wiki/Mind_flayer#Notable_Mind_Flayers
