We agreed to help him kill the vamp we have done so, our deal is with him is done. It on him for not specifying we will let him take her power, or that we won't just kill him alongside the vamp.
Dont even try to pull that fae shit here unless you explicitly want everyone to treat you like fae and double check every. Fucking. Thing. You. Ever. Say.
Implicit understandings are a thing in the setting, and the only people who try to pull this shit are villain-coded. Like the Reds.
Who exactly do you think would willingly do business with you?
Which minor practitioners will willingly engage with someone who is going to pull that shit when they so choose? Or do you think the wizards of the White Council will? Or even the White Court?
You are literally proposing blowing up what social reputation we have painstakingly built up for no good reason I can think of.
And picking a fight with half Essence in enemy territory against the person you came here with, while some of the people you were fighting are still alive.
Its a terrible idea on literally every level.
I'm under the impression the letter of our deal was to help him kill Arianna Ortega and we have done that.
It would be Fey to kill him but within our rights AFAIK.
See how almost everyone supernatural is warned about social engagement and deals with the Fae.
And why thats a bad thing for a social Exalt trying to socially engage.
And people dealing with us dont even get the assurance that the Fae cant literally break their word.
Trust is hard to build, and easy to evaporate.
There are real life companies that are rediscovering this in real time
EDIT
Besides, frankly, we wouldnt be able to kill him anyway before he could retreat.
Look at the amount of effort it took to kill Arianna, and she is not in the same power tier as a minor god of pain and terror.