Yes, IIRC that does have to be done before defeating Keara. FWIW I just got a minor upgrade for my creature's head from the chest past the ice wall (and a set of crappy legs). The axe that the ghost thinks about if you mindread him wasn't that great (possibly because Keara's fortress was one of the last things I did), and I ended up reloading and didn't bother mindreading him again.
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