Continuator
A continuator, in literature, is a writer who creates a new work based on someone else's prior text, such as a novel or novel fragment. The new work may complete the older work (as with the numerous continuations of Jane Austen's unfinished novel Sanditon), or may try to serve as a sequel or prequel to the older work (such as Alexandra Ripley's Scarlett, an authorized continuation of Margaret Mitchell's Gone with the Wind).