I tried the "destroy the death fog machine" route and the leak did indeed leak. I sent Fane in to loot and, in the midst of the death fog, there's Queen Justinia smashing the door and conversing with Fane (whom she had never met, none the less). The death fog had no affect on her. Conversation over, she disappeared. There was no body so I assume she made to Kemm's mansion. That's one tough cookie!
If she had dropped dead immediately after the conversation, Fane could have had a good line: "oh! Did I keep you too long?".
