William Golding, in Lord of the Flies, is intent on revealing the true nature of man, left to his own devices, without the benefit of civilization and rules to guide him.
The boys on the island begin their epic life lesson as innocents but the absence of "grown-ups" is an issue right from the beginning. Accordingly, a follow-up chapter could include the consequences the boys must accept as they are reintegrated into a society governed by adults. The chapter could be entitled "The end of Innocence" as Ralph "wept" at the realization and for "the darkness of man's heart."
The chapter would be sombre at the beginning as the boys, with Ralph as the main character, mourn their friends. The parents, after the boys have had some time, call a party thinking that the boys were all friends. As yet, unaware of the cause of Simon and Piggy's deaths, the parents believe it will help the boys who will enjoy reconnecting as part of their recovery because they are all very quiet and withdrawn.
At this point, you could add a little twist about Roger and how he has been in trouble with the police but has been allowed home as his behavior is presumed to be because of the trauma - and not his inherent nature. The reader knows otherwise and remembers Roger's "delirious abandonment" right before Piggy dies!(Ch 11)
The chapter could end (including descriptions of the boys' chosen attire) with the boys arriving reluctantly at the party and only because their parents insisted. This will also reveal the difference between making their own decisions on the island and their powerlessness now. There is a similarity as ,even when they made their own decisions on the island, they were still powerless when things went wrong.
The party is a fancy-dress party (perhaps) which connects to appearance versus reality. Jack comes as a hunter, Sam and Eric as intellectuals - in honor of Simon and Piggy - Sam carrying a Bible or religious book and Eric wearing glasses and carrying an asthma -like pump. Roger comes as "the Beast" (of course) and dresses in his interpretation - with a cardboard -made pig's head and a jar of flies - mostly dead. He shocks most of the other parents as the reader would expect. (Good versus evil is emphasized.) Ralph borrows his father's naval uniform - or parts of it but only because his mother says so. Ralph has always represented good moral leadership.
Ralph is uncomfortable in the uniform as he is ashamed of himself because, even as chief and with the conch, ultimately he could not maintain order on the island. Rules became unimportant and savagery took over. Even the officer who rescues the boys expected more from "a pack of British boys" suggesting that this is enough to guarantee good order.
The chapter would leave the reader in a contemplative mood.