Ok, so I finally, FINALLY found the crypts in the Skull Crags where Merabel's body is possessed. Holy wow was that an awesome boss battle.
Anyway, I went back to Gustav with his wife's body, and he still reacts in dialogue as if I haven't found her yet.

I hope I can ask this here: do I return the body to Gustav, and Im just experiencing a bad plot trigger? Or do I need to plant her in one of the sarcophagi in the crypts? Because the plot details are a little vague.

Thanks for your help!

I'll just say this: vampires don't usually drop a body you can carry around, they ____________________ .

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Mathus, Void Apostle of the New Moon

The suspense is killing me man!

That's the question you should be asking in game, that's all I'm saying.

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Mathus, Void Apostle of the New Moon

I think I was able to fill in what goes in the blank. I just have to fight my way back there.
And I will ask in game too, as I really enjoy the roleplay experiences Ive been having lately. Very cool people in Amia.
Also, I think I should have taken 'undead hunter' for my job ranks, instead of what I did take, considering the amount of undead Ive been coming across.