I find it hard to believe that this question is correct.  I really do not think that Mafatu ever does let his fire die out.  I say this because I do not remember any place where that happens and I cannot find it when I search one of the searchable versions online.  Looking through my copy, I can't find it either.

I would also point out that he clearly says that he must not ever let it die out.  You can see that right at the start of Chapter 4.  I thought maybe he let it die off when he decided to go home, but he does not.  Then I thought maybe he let it die when he heard the cannibals, but it does not say he did.

Message me if you have more information -- like if you have a worksheet, what is the question before this one so I can know more about where this should be found in the book.