My eyes have filled with tears. How on earth do you explain death to a one-year-old?
You don't. It's not yet possible.
The stories of love and the pictures will have to be brought out on a regular basis so the child can feel a connection long before it understands what death is. Then the death is almost secondary and the child will have mostly happy thoughts; manufactured memories are no less powerful and meaningful than 'real' ones. I know that sounds very glib. I don't know how else to put it. This is a very sad thing, but it's important to fill the gap, gently, to minimize future negative experience. All this happens to help the adults involved in the matter as well. (I'm no expert, I should add)
I remember many beautiful things from my childhood, but I realize that I only know them thanks to the videocamera or camera or tape recorder or adult human noggin that recorded them to remind me that they took place. I was, after all, 2 years old or so for them, but they do genuinely feel as if I remember them, and they are good for me.