Just like how the option was added to have both Halsin and Minthara join your side, I please want to make a case for an addition be made that the player can talk the Emperor down and be able to side with both him and Orpheus against the Netherbrain.
Most likely, it would be an incredibly difficult saving roll, but it can be done. I even want to explain how it would make sense in the narrative.
Just as how you talk to your Companions and have your bond to them make them trust and side with you more, if you treat the emperor well, and gain his trust, that could also be a potential unlock condition for this, as your bond with him will be strong enough to convince him.
Currently in the narrative,
the Emperor believes that Orpheus would kill him and the party on the spot if he is freed. All of his actions are done in self preservation, as his end game interactions shows that he is a true neutral character. This is the reason as to why he decides to join the Netherbrain if the player says they wish to free Orpheus, as with the Netherbrain he truly believes that he has a chance for survival, and that freeing Orpheus will lead to his immediate death. He has already escaped the hive mind twice. Why shouldn't he think he can escape it again for a third time after the storm has calmed down.
However, the Gith Prince
shows that he is open to reasoning, and I legit believe that if him and the Emperor were to meet, they would be able to come to a truce due to the situation.
In fact,
a pact between them would be extremely beneficial, as the Emperor will see that Orpheus is open to reason and having him join the party will be much better for his goal of surviving the Netherbrain than his original plan to rely just on the survivors and Orpheus will know that he needs an Illithad to use the Netherstones, so he will need the help of the Emperor, instead of needing to become an illithad himself.
This ending would allow for the best outcome for everyone, as Orpheus and the Emperor could start a alliance between the Githyanki and Illithads that would empower and preserve their future empires to come. (That is if Orpheus is successful in overthrowing Vlaakith.)
I mean, if you side with Orpheus and become an Illithad so that he doesn't have to make the sacrifice, you can ask him to promise to tell his people that not all Mind Flayers are the same. Orpheus is open to diplomacy with them.
I don't know if anyone would like or agree with this, much less if any of the devs would see this, but as my mother always said, you miss every shot you never take. Let me know what you think please!