Since some of y'all are getting confused, let me explain the ending to you. The reason the ending doesn't explain who's to blame and where's the girl is because both main protagonists are consumed by their own guilt and have made this tragedy be all about their own egos. It is so important for each to prove they're not guilty, that the husbands and the daughter don't matter as much. This is why we don't even know how Hee-ju's husband looked, let alone what his personality was. The fact that she had repressed the memories of her strained relationship with him, or that Young-nam had not even noticed her husband's suicidal tendencies should give you a clue. It doesn't matter at this point whose fault the accident was, this is why we see so many different sides adding their own blame to the cause. All these "twists" are there for a reason. The movie is basically saying that such disasters happen due to a combination of factors, and it's ridiculous to blame one person. I'm not gonna say what the deer (or fawn) represents. I have my hypothesis, but I think things like this should be interpreted by each viewer individually. What I will say is that the encounter with the deer must've been a revelation for the protagonists. This is why we don't need to know what happens next. It is all about their realization. Their story arcs end there.