.... and it would be no suprise if the tree-owner would actually win the juice in a court-case .....
Just because something is laying unused doesn't mean taking it is any less theft.
Hyperion only had a very limited project, and a clear contract with that buyback-clause in it. Everything they did on top of that was at their own risk. A judge may order them to only transfere what was orginally planned, but cutting OS4 back and still keeping working might be quite hard, and offcourse it wouldn't give them the rights to do anything with the rest.