Imshael is the boss you encounter in Suledin Keep in Emprise Du Lion. When you come to face with him, he’ll pitch you that instead of attacking him, he’ll give you either Power, Riches or Virgins (Call me Ishmael quest).
After picking one of the options(except killing him), a loot jar appears where you can get the rewards.
Here are the rewards of each choice:
For power, you will receive Pure Spirit of Essence, Amulet of Power for Cole, and a unique shield called March of the Everlasting.
For riches, you will receive 4 gems (Sapphire, Pearl, Diamond, Emerald) which you can sell.
If you select Virgins, he’ll say he doesn’t really have any virgins, but instead will give you a “powerful” rune if you so choose. This rune is a Superb Corrupting Rune.
You’ll still be able to take Suledin Keep if you chose not to kill Imshael.
However, choosing not to kill Imshael will make Blackwall (or some other party member) greatly dissaprove and Michel de Chevin (the captain you encountered outside the starting camp) will be dead when you visit him again. He would become an agent if you chose to kill Imshael.
What about killing him?
If you do decide to kill Imshael, he’ll turn into a demon. And, turns out the loot he drops is the same rewards as Power:
So its just better to kill him!