So am I correct in saying the gateway gives no guaantee that a message a controller asks it to send will actually reach a node ?
Presumably you would have to have a sensor on the node that could read the state of the switch so the controller could send the message then conform it was received.
It would be good in that event to have a ping capability on the node so that if the node loses communication wih the gateway (or controller) that it could put itself in a default state. In the case of a sprinkler, that could be an off state.