I've watched the birth by sleep cutscenes and understand Ven's ultimate fate: he has an internal fight with Vanitas, and defeats his dark half. Vanitas fades away in balls of light, and Ventus falls into a deep sleep.
Is the removal of Vanitas REALLY the reason Ventus is asleep? Think about it carefully. When Ventus was first separated from Vanitas by MX, he was able to become a Keyblade wielder by forming a bond with Sora. He didn't have to become part of Sora. So why did he fall into a coma when he defeated Vanitas inside of him at the Keyblade Graveyard?
Is the removal of Vanitas REALLY the reason Ventus is asleep? Think about it carefully. When Ventus was first separated from Vanitas by MX, he was able to become a Keyblade wielder by forming a bond with Sora. He didn't have to become part of Sora. So why did he fall into a coma when he defeated Vanitas inside of him at the Keyblade Graveyard?