This is an interesting question. The answer, of course, must be your own; however, there are several things to consider when deciding where William Golding's story Lord of the Flies might go after the naval officer arrives to rescue the boys.
First, do you assume that the boys were, indeed, rescued? It seems nearly certain that the officer took the boys from the island; however, something might happen to the ship (it is a military vessel, after all) which keeps the boys from returning to the "civilized" world.
Second, do you assume that the boys will return to their own homes and lives without ever confessing to any adults (or courts) what happened on the island? If so, you might follow each of the primary characters as they try to adjust to their former lives. Certainly they will have to deal with their private guilt and shame.
Third, do you assume that the boys will have to be punished for their crimes? If so, how will they possibly be able to make anyone understand what happened on the island, and what punishment could the adults administer which would do any good?
Finally, how do you see any or all of the characters changing after they leave the island? If so, you have the potential to create different characteristics for each boy based on how they respond to what happened to them on the island.
In short, you must take what you believe about what happens next to these boys and demonstrate your hope--or hopelessness--about their futures. Consider Ralph's final thoughts:
Ralph wept for the end of innocence, the darkness of man’s heart, and the fall through the air of the true, wise friend called Piggy.
How you feel about the loss of innocence, the evil which resides in the heart of man, and the deaths of three innocent boys will determine what you think happens to them next.