No you don't, anyone is able to start a chat and send a message to anyone else regardless of whether you are or aren't connected.
Chat: These are messages between two attendee's/users. Message: A message is sent from an organiser directly to an individual user or users. Push notifications: A push notification appears like any other notification from an app (Such as a news, gaming, or social media application). It can be from the organiser to notify/remind you of something, or generated by the app to let you know of something happening inside the application, such as a received message or request for feedback.