Q. When referring to a zombie, should I use the relative pronoun who (which would refer to a person) or that (since, technically, the zombie is no longer living)? Essentially, does a zombie cease to become a “person” in the grammatical sense?
A. Let’s assume this is a serious question, in which case you, as the writer, get to decide just how much humanity (if any) and grammatical sense you wish to invest in said zombie. That will guide your choice of who or that.