An interesting literary question was posed in an article published today in BBC News Magazine (http://www.bbc.co.uk/news/magazine-16510376). The article asks whether or not it's proper for one writer to complete the unfinished work of another. The author prompting the question is Gwyneth Hughes and the unfinished work is Charles Dickens's The Mystery of Edwin Drood. Hughes wrote an ending to the novel and adapted it for television.
I'll withhold judgment on Drood until I've seen the drama, but in general I'm not in favor of what the article calls "literary necrophilia." For authors to capitalize on the reputation and intellectual property of another is...well, theft. It's prevalent nevertheless. Witness the recent resurrections of Sherlock Holmes and James Bond--extensions of the work of Doyle and Fleming by those who are not Doyle or Fleming.
In another genre, the question has an easy answer. No one would dream of fashioning new arms for the Venus de Milo or of completing one of Michelangelo's unfinished marble sculptures.