In Bioshock after killing Big Daddy I can’t find the Little Sister he was protecting. Is it possible she was killed, or one of the NPC got her?
No, but it is possible the Big Daddy wasn’t protecting any Little Sister.
Big Daddies roam Rapture and get Little Sisters from the vents, but you can kill them before they are protecting any of them.
If he was protecting one, she should stay near the deceased Big Daddy, they cannot die nor be taken by any other character.
Source : Link , Question Author : Piaskal , Answer Author : juan