Well it's not just Minthara. Everyone fights to the death in BG3.
I've actually seen it once, I believe. After killing Lump when he turned on me, his surviving minion ran out of range and despawned. It was replicable across two different runs of that fight so it seems that there may be at least one instance of enemy flight in the game.
The leader of the goblin group who torture a gnome in the village always tries to flee, once his health is dropped to 0 (not 1, unless I was mistaken). If he's allowed to flee, everyone else flees too, which makes me really hate him because I don't get XP for watching them unstoppably run away. So, whenever I'm here, I make sure I'll kill everyone else first before chopping down their leader. However, this makes the battle much harder for a party of level 3, who wish to fight them fair and square. That's because this leader is by far the most vicious among the group. Keeping him alive means letting him attack/slaughter my party members with no consequences until all other goblins are dead.
