The Heroes predated the Calamity? That would be the smoking gun that Jack has been waiting for, to prove Kalki's theory at last. It still doesn't excuse a single action that she's taken. But it would finally make some sense.

Jack's eyes darken at Chrom's questions, the very same ones he wants to ask. "Why wouldn't they leave?" The question is tinged with guilt. "And how can we keep the same thing from happening to the next city?"