It is possible to have both characters killed and by doing so follow the Githyanki protocol, but it's not a straightforward path a Githyanki would expect. You'll have to bend it a bit to accomplish the end result.
To answer the question; if she's loyal to Vlaakith then the Emperor can freely consume Orpheus without her interference, in fact she'll be overjoyed to watch him die as she's dutybound to ensure his death, but you won't be able to kill the Emperor anymore after that point.So if you're looking to have both the Emperor and Orpheus killed while remaining loyal to Vlaakith by following the protocol, then;- You'll have to betray the Emperor when the time comes by freeing Orpheus
- Lae'zel will become extremely pissed off for not following Vlaakith's protocol to the letter, forcing you to pass a massive (30) persuasion check to remain your ally (so be sure to come prepared with Charisma buffs)
- Make Orpheus become a mindflayer
- Kill the Emperor in the final battle
- Destroy the Absolute
- Allow Lae'zel to kill Orpheus afterwards
- And you both will ascend with the protocol followed
There is no way;- To have Orpheus killed by the Emperor and then killing the Emperor afterwards.
- Or killing the Emperor and not having loyalist Lae'zel kill Orpheus afterwards, which she's dutybound to do.
![[Linked Image from bg3.wiki]](https://bg3.wiki/w/images/thumb/d/d4/Minthara_Approval.png/26px-Minthara_Approval.png)