
He really left the ending open. Maybe so he would have the option of adding more later. He didn't ever say much about what Eragon would do and while it may have been for the reader to decide I think he may have been unsure what to do so he left things open. In a fifth book, if he ever wrote one, I feel like the plot wouldn't be a continuation of the story line we have had but it would either be in the far future or back to the start of all the corruption in the riders.