If interviewed after his rescue, what would Ralph say are the causes of Piggy's and Simon's deaths in "The Lord of the Flies"? Would Ralph tell the...

When considering what you will write, be sure to maintain verisimilitude.  That is, keep Ralph in character.  To do so, perhaps, you want to reexamine the second to last paragraph of the novel:

For a moment he [Ralph]had a fleeting picture of the strange glamour that had once invested the beaches.  But the island was scorched....Simon was dead--and Jack had...The tears began to flow and sobs shook him.  He gave himself up to them now for the first time on the island; great, shuddering spasms of grief that seemed to wrench his whole body....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.

Judging from this paragraph, it seems in character for Ralph to be very truthful. (Do not forget that his is the British society of Australia that does have great respect for honor.)  In addition, his love for Piggy, especially, should provide the impetus for him to be very candid.  And, it seems that after Jack and Roger have burned the island and attempted to slaughter him, Ralph will have no problem in implicating them in their attempts at murder.  Probably, Ralph will mention the lack of adults and the fears of the small boys, their imagining of a beastie, etc.  These extenuating conditions may help to mitigate the descent into savagery by Jack and others.  However, in the British society of the 1940s, there would not be too much leniency.

So, with these ideas in mind, you can devise your interview as we editors do not write for you.  But, here is an example that may get you started:

Q:  All right, Ralph, we understand that you and the boys were stranded for ___months after the plane crash.  Tell us, now, what happened after all of you were there on your own.  Were there tensions among you?  You have said that you were the leader, but was there some rivalry with another boy or boys?  What happened?

A:  Jack Merridew was the leader of the choir.  From the first, he wanted to be in charge of his boys.  Later, he said he would be the hunter and kill the pigs that were on the island.  Well, there was another mean boy--Roger--who liked being a hunter.  I mean, he liked to hit and hurt.  Uh,....

(There should be some hesitancy on Ralph's part, so have the interviewer, who is an adult, draw the truth from him as Ralph tries to circumvent the brutal truths.)

Good luck!