Hi,
You can indeed receive a callback when an event has finished playing after having been released. The callback type FMOD_STUDIO_EVENT_CALLBACK_TYPE.DESTROYED will trigger a callback specified by Studio.EventInstance.setCallback() when an instance is just about be destroyed. Passing your dictionary to the event instance as user data with Studio.EventInstance.setUserData(), and retrieving it with Studio.EventInstance.getUserData(), will allow you to remove the instance from the dictionary within the callback.