$20 million at stake here turning on the question of whether the Darth Vader and Stormtrooper helmets attract the protection of copyright. If they do then the designer retained copyright as it was not transferred - if not then his rights were lost in his contract with the producers.
Amusingly the idea which has twice not worked in the UK courts but our American friends are having a crack anyway is that the helmets have a utilitarian purpose and are not works of art. Perhaps they are thinking of selling them to the MOD / SAS etc for raids into foreign lands so that when landing in Libya in the dead of night they can whisper / breathe "Luke I am your Father" and send the local militia packing.
Personally the helmets appear to me to be original and artistic works and George Lucas simply dropped the ball not getting the paperwork in order at the start.