Less than two months before ”The Lord of the Rings: The Return of the King”’s Dec. 17 opening, even the most wary and sequel-burned of moviegoers assumes the third Tolkien installment will be a masterpiece. And why shouldn’t they? It was shot concurrently with the other two near-flawless installments, which were mostly faithful to the same written epic that King will be concluding. But let’s consider this heresy: What if something goes horribly awry? Don’t forget wrong turns by other fanboy-fave series in round three: What if cutesy animals or tykes rush in to save our Middle-earth heroes, like ”Return of the Jedi”’s Ewoks or ”Mad Max Beyond Thunderdome”’s lost children? Or Frodo shaves his head before luring Shelob into a molten-metal jacuzzi and committing suicide, a la ”Alien 3?” And if Gandalf somehow ends up in the Old West like ”Back to the Future Part III,” we’ll tar and feather Peter Jackson. Sure, this is all unlikely, and King will probably rule, but it never hurts to lower your expectations. Nobody wants a relapse of ”The Matrix Reloaded” heartbreak.