What does it mean when you dream of someone who died but you dream they aren't dead?

Such dreams are very common, representing the subconscious mind's struggle to accept the reality and finality of the death. If the death is recent, the dream is a natural part of the mourning process. In other situations, the dreamer's memory of the deceased may have been triggered by a familiar place, a piece of music, or many other things. See the attached link for further discussion and examples.