To be fair, it's pretty clear from prior explanations and evidence that she's still a person. I don't know where her creator got her soul (or did all sludge have a soul all along?) but subjectively speaking she definitely had one; all that's missing is her human form. And it's really hard to imagine with that cast of friends, that no one's going to be able to find her and bring her home.
It is a godawful cliffhanger, though.