OK, im using my license in On-Demand mode. Am I really connected permanently to the Altium Server hosting the licenses?
You do not remain permanently connected to the Server. Altium Designer communicates with the Altium portal by making a request and receiving a response. At that point the connection is closed. There will be numerous requests to sign in, request the available licenses to display, and so on, but each request is independent and then the connection closes.