I was hoping that the pact with the devil would be just a legend, and that the whole family would have to grapple with the fact that they've lived a lie their whole lives and that their murders were completely pointless. So, I was disappointed when people started exploding. It felt like an easy way out, but it was vindicating for Grace.
I really loved the ending! I don't think that the family would have changed their ways even if the whole pact with the devil had been a myth. They would have found some way to justify their actions and they would have continued being awful people. It was really satisfying for me to watch them explode.