This app will attempt to refresh the node, and optionally operate the switch. If the node has left the mesh, then the refresh/switch operation will fail, but the app does not send an alert to that affect.
There are other community apps that send idle alerts. I have one that I use (Simple Idle Alerts) for time critical devices:
Given that Simple Idle Alerts is one child per device, it's not intended for broad scale monitoring. For broad scale monitoring, here are a couple of apps that I would suggest:
