ToME: the Tales of Maj'Eyal

So, playing a skeleton Archmage on Nightmare. I cleared the first area of the Grand Corruptor's area and then left to do other things. When I came back, I entered to second and final screen for the first time and the mid-fight dialogue with the Corruptor appeared immediately, though he himself did not. I cleared the area and he was nowhere to be found.

What is to be made of this?

Something probably killed him, most likely an elemental randboss. It's possible although highly unlikely.

Really? Well that's fun. I've seen it in other areas but never there. Thanks.