Over the course of its lifetime the Star Wars movies have grossed $4.5B worldwide not adjusted for inflation. Disney released some other numbers to help analyze the transaction: consumer products licensing revenue for Lucasfilm is expected to be $215m in 2012, and in 2005, the last year a film was released, EBIT was $550m. That implies about 5-8 films to make back the purchase price (depending on how much you assume they make in a non-film year). At 1 film every 2-3 years call it a 10-15 year payback period.
|Source: Box Office Mojo|