It has been a while; if/when I ever revisit Juice Galaxy, I'll need to rediscover that myself.
The two guesses that come to mind for me are:
1. You'll have to save your game, then go to the main menu, then reload the game. The juice student should respawn at the fountain in the graveyard; and/or
2. You need to collect the pieces of paper and then (SPOILERS); then either by speaking to Mr. Fox's kid self or by interacting with his bed, you'll be able to return to the world of the waking.