No matter how ridiculous or farfetched plot twists Nomura has whipped up, I'd only lose the joy of playing if my fave characters were to die. Probably wouldn't be able to finish the game at all.
There are, however, couple of things that would disappoint me. Radiant Garden, including the castle, not being playable would make me really sad. I absolutely loved running around the world in the first KH, the level design is still a favorite of mine.
The beforementioned mini-games. Yikes. I don't recall ever enjoying them. Please don't let there be an annoying one we have to play in order to proceed.
Kairi not getting a bigger part. The poor girl's been neglected for too long! She's got a Keyblade now, just let her use it. Also I'd like to know more about her past and see her reunite with her grandma.
I want to see more casual chatting, characters telling funny stories about what has happened to them when they were x years old, what they like and what they don't, basically just fun trivia scattered here and there. Like, maybe when Sora has finished cooking something with Remy, he'd mention the food he just prepared was Kairi's favorite? Now that Sora has the gummiphone I'd like to see him get messages from his friends and family. Imagine Riku boasting about finding something cool or Sora's mom asking if he was wearing warm clothes and remembers to eat regularly. Keep in touch, people!