They started reshooting some scenes for the next episode some days ago..........could be they change the story to let Leia die/disappear at the end of the movie or just because they needed more extra footage. The movie was already roughly edited, and John Williams is now recording the score.
As far as replacing actors.....Jonas Suotamo has officially followed up Peter Mayhew to play Chewbacca.
http://movieweb.com/star-wars-force-awakens-chewbacca-actor-joonas-suotamo/