I loved how they handled Barbara:
She didn't have any friends except Nancy, the town had already spent a week hyping up Will's disappearance, and we didn't see Barbara's parents as much as we saw the kids, so it made sense that the boys' relief that Will came back would be larger from a narrative perspective than Barbara's parents' and Nancy's grief at Barbara dying.
More importantly, the writers didn't downplay Barbara's death. The characters downplayed her for the reasons above, but Nancy didn't downplay anything, and you could just feel her isolation at having to be the only person grieving that her friend didn't make it, while surrounded by people celebrating the boy who did make it.