It all depends on how much of the movie that they have completed. With The Crow, Brandon Lee died at a point in the movie where they altered the ending and provide a stand-in that was never shot up close. Interview with the Vampire was in production with River Phoenix playing the role of the reporter interviewing Brad Pitt. After he died during filming, they recasted the role with Christian Slater and reshot all scenes in the hotel. It was released with Christian Slater in the role. He did a very good job in the role, but it would have been interesting to see how River Phoenix would have played it. He was very talented.