Well we know the Sith are going to lose within the next two thousand years. As people have said, due to the wars all the history of this era was lost, hence why we can have Chiss in the empire in TOR and yet no one knew what the Chiss were post-Eps. VI till after Thrawn showed up. For all we know the Sith empire obliterates the republic who is forced back into the Unknown Regions. The Republic finds a gigantic *insert superweapon here* comes back and reclaims control of the galaxy. It's all possible :P