what do you think happened to the boys once piggy died? Why?

Ah, for this you need to read the end of your novel. Or simply check out Gradesaver's summary.

"When Ralph looks up, he is surprised to see a figure looming over him. He realizes that the figure is a man-a naval officer! The officer tells Ralph that his ship saw the smoke and decided to investigate the island. Ralph realizes that the officer is under the impression that the boys have been only playing games. The other boys begin to appear from the forest, and the officer begins to realize the chaos and violence among the stranded boys. Percival tries to tell him his name and address but finds he can no longer remember it. Ralph, informing him that he is boss, is sad to find he cannot answer the officer when asked how many boys are on the island. The officer, aware that they have not been behaving according to the rules of civilization, scolds the boys for not knowing exactly how many they are and for not being organized, as the British are supposed to be.

Ralph insists to the officer that they were organized and good at first. The officer says he imagines it was like the "show" in The Coral Island. Ralph, not understanding his reference, begins to weep for the early days on the island, which now seem impossibly remote. He weeps for the end of innocence and the darkness of man's heart, and he weeps for the deaths of Simon and Piggy. All of the other boys begin to cry as well. The officer turns away, embarrassed, while the other boys attempt to regain their composure. The officer keeps his eye on the cruiser in the distance."