Gorgik is using:
<worn around neck> a key made of ice

When he dies, there's no key in corpse.

In my (limited) experience the mobs there do different things if you are too high a level. There is an echo of him chucking the key to the east (where lava and fire elementals are) destroying it (cause it's made of ice!)

I've missed the echo before, maybe that's what happened here?

I am unable to reproduce the issue thus far using both slay and actually killing the mob.

*snip all the room info about said mob cause its in an area explore*

Gorgik paces angrily about, muttering a constant streak of curses.

slay gorgik
You slay him in cold blood!


exa corpse
A pile of fist-sized chunks and loose organs are all that remain of Gorgik's corpse.
The corpse of Gorgik contains:
a key made of ice

get key corpse
You get a key made of ice from the corpse of Gorgik.

I thought the same thing at one stage.

Hopefully i am not revealing to much. But pay attention to some of the things you are doing while fighting.