There is a system variable (available in the formula editor) systemVars.networkStatus with one result being "none". So you could use a formula IF(systemVars.networkStatus == "none", message_for_network_error, message_otherwise) to toggle the content of an error.
You can also use an IF logic function and set the condition to systemVars.networkStatus == "none" and the use the logic functions Hide component and Show component found in the Flow function market to toggle what components are shown.