Not everyone can handle the trauma of being killed then resurrecting so I can't fault her for giving up & of course he feels responsible since they're stuck together until the boss is dead. Can't wait to see how he'll handle it & most likely she'll come in to assist when things get grim.
I don't disagree with you...However, it feels like it lacks in a poetic sense.
When the guy wanted to leap off a building to put an end to his cyclic suffering, the girl pulled him out of it. It should also be his responsibility, now, to return the favor and pull her out of her hole, and not let her despair.
That being said, that's just in "a poetic sense". It just feels "right" for it to happen, but it doesn't mean it necessarily should happen. The MC wasn't exactly a walking beacon of morality, hope an dreams, either. That was her job.