I think the master sword will return because I believe that this Zelda game will take place during the time they mentioned in WW where ganon comes back and then the hero dosent rise again beacuse the teaser as darkness reigns will the hero rise again or will darkness reign? Also to back this up in Oot the master sword was placed in the temple of time and in WW when you go down under it is in the castle so it had to of moved during then IF this game follows the OoT, MM , WW timeline. And theres no way thats Ganon its probably just a fire boss.