We are not talking about the main scenario. The topic is about the five short stories about the Calamity. No matter what anyone assumes, in those short stories there is no mention of Bahamut's fate, the star of the battle. That is simply bizarre.
I'm very well acquainted with the "What do we do now? We bury the dead and heal the living" motto. And yet, over the week or so these stories transpire, the weapon that kill the remaining survivors and obliterate your town gets no mention. Any commander would definitely be more worried about the enemy he cannot see.
What makes you think Bahamut simply dissolved into the aether?