"I think (a) memorial may be a good way for the family and communities who have been touched by this tragedy to move toward closure and healing,"
I don't think in this case there is really any such thing as "closure". Even not knowing these families personally, there is no sense of finality to it. It may sound odd, but a widow's emotional thinking would be to deny it, no matter how impossible it may seem. A case of "there is no body. How do I know he is not coming home tomorrow?"
I really don't know how to bring about some sense of closure in this situation. They will never be able to provide a "cause" of death, a body, etc. But you can't very well ask someone else to go back in there, to risk their lives to recover bodies. Because at this point they are almost certainly deceased.
My heart and prayers go out to everyone involved in this tragedy.