Everything stays in your portfolio until you dispose of it (sell or cover) or it is delisted.
As actors exist in their own right outside the films they star in, they do not delist when the movie they appeared in delists - only when they haven't been attached to anything for a long time or have passed away.
If you want them to go automatically, then you need to use the Advanced Trade to set-up a Limit Order for the amount you want to sell/cover them at.