A friend’s teen daughter died suddenly several years ago due to a severe infection. She was otherwise healthy ... this happened completely out of the blue. My friend’s faith is shattered by loss and grief. If God controls everything, from a leaf falling to our yearly income, what is God doing by causing and allowing her death?
I am so sorry to hear of your friend's loss - it must have been devastating and I hope and pray that he and his family will be able to overcome their grief and to experience joy and happiness again.
We believe that God loves us and is with us even in the midst of the most terrible suffering and tragedies. Sometimes the tragedies can be self-inflicted, sometimes they come through other people's free will and sometimes they appear to be directly from God. Suffering is not necessarily a punishment for sin; it can sometimes be a means of growth, a test, or a means to perfect one's World to Come. I pray that things will improve in the lives of your friend and his family and that they will find comfort.
I don’t know if they are ready, but they can try to read two wonderful books that may help them deal with faith, tragedy and tests. One is called Garden of Emunah by Rabbi Arush, and the other is called Why Me G-d? A Jewish Guide to Coping with Suffering by Lisa Aiken. (Both are available on Amazon.com or at Jewish bookstores.)