What are the pros and cons of a book where the antagonist wins and/or the protagonist loses? How would it affect a story? And what about sequels? Would you set up a trend of sadly ever afters(like in the A Series of Unfortunate Events by Lemony Snicket), or will the main character go ape**** after finding out that Evildude managed to get the Supercallifragilisticexpialidocious Ring of Infinite Power, and hunt him down with a chainsaw(or a laser gun, or a sword) and attack him in book 2? This first sadly ever after will probably affect your entire book series(if there is one, and yours is not a standalone book), namely because Evildude has the Ring of Infinite Power, and transforms into a clone of Chuck Norris, except 10 times stronger.