SilverWook said:

The studio would have found a way to wiggle out of it if there was enough money to be had.

Look how Beneath the Planet of the Apes ended, and Fox still found a way to make sequels.

Best ever example. If I ever teach screenwriting, this was the example I plan to use.

Well that and the incredible story of how James Bond returned in You Only Live Twice to a Spy Who Loved Me which became The Spy Who Loved Me in a Moonraker aka Goldfinger '77/Thunderball '79. The rough elements are the same sadly.