Comment on the denouement of "Lord of the Flies". Is it realistic?
Yes. I think the denouement pulls an amazing trick. The reader has completely accepted Ralph, Jack and the boys as adults: you forget how young they are. And the way the ending makes its impact is by shifting the narrative focus - no longer do we see things through the boys' eyes, but the camera pulls back and puts an adult in. We realise - horribly - that these atrocities have been committed by little boys.
Here's the moment it happens:
Then he [Ralph] was down, rolling over and over in the warm sand, crouching with arm to ward off, trying to cry for mercy.
He staggered to his feet, tensed for more terrors, and looked up at a huge peaked cap.
The naval officer also locates the boys back in a civilisation at war, and "in ruins": he even has a "sub machine gun" on board his ship. It reminds us that these boys' violence is located within a world which is very violent at an adult level. And these boys are the product of something.
Golding hammers home how small they are:
Dumbly, Ralph shook his head. He turned a halfpace on the sand. A semicircle of little boys, their bodies streaked with colored clay, sharp sticks in their hands, were standing on the beach making no noise at all.
Ralph nodded. The officer inspected the little scarecrow in front of him. The kid needed a bath, a haircut, a nose-wipe and a good deal of ointment.
These are little, little boys. And at the end of the novel, with them all in tears, Ralph cries for the "end of innocence", and "the darkness of man's heart". It is a return to reality, a horrible realisation that this is not a symbolic novel but a naturalistic presentation of young boys creating hell for themselves. It's a harrowing denouement.