That is mergers and acquisitions 101. Look at any mining or chemical company that merges itself into a new entity without taking along its abandoned worksites in need of environmental reclamation.

The interesting part is Lucas's role in all of this. I want to see the purchase contracts. It might actually say in there that Lucas was supposed to buy out these rights and deliver the assets clean of obligations. If I were advising, I would say sue both Lucas and Disney and let them fight it out amongst themselves.