What does it mean when you dream about someone dying?

Dreams are about the dreamer. So if someone else dreamed about you dying, the dream concerns that person, not you. Please refer to the site linked below for more information on dreams about death.
Dreams are about the dreamer. So when someone else has a dream about you, it means that their sleeping mind somehow chose your image to symbolize something about the dreamer's own life. Dreams also communicate through symbols. In dreams, death and dying usually represent an end of something - a job, a relationship, a school term, a vacation... as well as the beginning of something new.

---- It could mean that they care about you.