If you choose to disconnect, you will no longer be able to manage the disconnected computer from Forefront TMG Management.
To reconnect, right-click Microsoft Forefront Threat Management Gateway in the Forefront TMG Management tree, and select Connect to. Then, connect to the local server on which Forefront TMG is running, or to a remote server. Management permissions are required on the remote computer. You can connect to the remote computer using the credentials with which you are logged onto the local computer, or specify alternative credentials.