Well it's not just Minthara. Everyone fights to the death in BG3.
I wish they would have included at least one returning nemesis who would have the sense to flee and plot their revenge. Lorroakan fits the bill pretty well as a powerful mage who could teleport away. Then again he's not a well crafted character, more like a childish cartoon villain or a caricature of a fancy evil person. It's hard to imagine a person like that who clearly lacks any kind of serious conviction would become a powerful enough Wizard to kidnap a demi-god. Potentially a fun enemy, but a really weak character overall in his current form.
