Ok, 3 things.
First, who ever said that this encounter was ever meant to end in a tpk? Not me. Not anyone I read mentioning this encounter. Bahamut is a benevolent god, not a moronic asshole like murder hobos.
Second, murder hobos are not playing to win, they're playing moronic assholes in a power fantasy. But anyway, both murder hobo and playing to win make problem players.
Third and finally, this encounter is a narrative tool that can take a campaign back on track. A discussion alone doesn't have this power, because the characters changing their behaviour suddenly would break the story.