What does it mean when you dream of someone dying who isn't dead yet?

could mean many things .

Another response:

Dreams use metaphors. This means that something that happens in a dream points toward something else. Generally, dreams about death are about changes in the dreamer's life. If the dreamer's parent or grandparent dies in a dream, it probably means that the dreamer's life is changing from childhood toward adulthood. Often dreams about a friend or lover dying actually refers to a part of the dreamer's life that is completed or drawing to a conclusion. For example, a high school graduate might dream about a student dying. That is an image of childhood coming to an end.

So think about your dreams in the sense of what is represented by the persons who die in the dreams.