hopefully he gets a new outfit for KH3, maybe he was testing the organizations coats, since they're supposed to protect you while traveling through darkness, and something went wrong and his heart was swallowed by darkness.
It has been really bugging me lately, how did Lea and Isa become nobodies? We already know that it happened in Ansems lab on Radiant Garden, since that's where Lea woke up after being recompleted, but what exactly happened? Its also weird that he is wearing an organization coat when he wakes up, I wonder if there is a connection between that.