Piggy is sacrificed to the forces of destruction and chaos, represented by Roger's stones and the boulder, to all consuming sea. What does this event symbolize?

Piggy's death is also the death of knowledge, order, and civilization and, to a large extent, goodness. Most of the boys never valued Piggy even though Piggy held their best chance of being rescued. He was the source of knowledge as well as the literal source of light/fire, through his specs.