User blog comment:Bears1234/Destruction of the Dark Brotherhood, a review/@comment-30303790-20120223065338

I think they let Cicero and Babette slip away so that they could continue the DB's story in Elder Scrolls: VI, and by having them absent it means you do technically destroy the DB as an organization...just not permanately.

Also Babette, despite technically being hundreds of years old, is concidered a child by looks, and any third party who sees the decapitation (because you know it would flood youtube) would take this completely out of context. Bethesda was probably just trying to avoid an potential flak.