In Chapter 2 what does the disappearance of the small little boy do for the plot of "Lord of the Flies"?

In Chapter 2 of "The Lord of the Flies," when the boy with the mulberry mark disappears during the distraction of the raging fire, credibility and perpetuation of the accounts of the "beastie" by this very boy are ensured. For, the explosions of this fire send creeper vines to fly into the air, appearing much like the snakes that the small boy has imagined:

A tree exploded in the fire like a bomb.  Tall swathes of creepers rose for a moment into view, agonized, and down agains.  The little boys screamed at them. 'Snakes! Snakes! Look at the snakes!

Also, the loss of the boy from the power of the fire exemplifies that uncontrolled power can cause chaos and even death. This is a foreshadowing of what occurs later in the novel as uncontrolled power by Jack and Roger does, indeed, effect chaos and death.  In fact, Golding writes of acres of "yellow smoke" rolling toward shore indicating that evil [yellow is the color that symbolizes evil] will encompass the island.  In another hint, he writes,

Beneath the capering boys a quarter of a mile square of forest was savage with smoke and flame

Added to this, Piggy is much disturbed by the boy's loss as he feels an adult reponsibility and Ralph feels "shame."