The lights of the henges are either destructable or you can turn them off. I didn't pay attention to which it was. It happens if you melee them twice. Perhaps this could be part of the henge. Perhaps removing evidence of the henge, AKA playing co-op, killing engineers. removing pliths, getting rid of elites, and destroying all the lights could lead to something. We keep adding things to these henges, well maybe we should be making them barren.