Sora is the official Key Blade weilder, unless they plan on going through all the trouble of finding a new weilder and Sora going into retirement, Sora will still be the main. KH is Sora's story...besides, in the ending of KH2 there's the letter the three recieve from the King. This hints to Riku, Sora, & Kairi still being in the next game.