I get battery low alerts on my sensors periodically showing 1%. But then they go right back up to normal. The question is: if a battery died completely, would ST know? Or would lack of communication from, say, a water sensor, not cause any notifications? I’m worried that if a water sensor battery does die, ST won’t know to notify me. Is there a definitive way to know what ST would do in that case?
You are most likely correct, that you will never know.
There is a SmartApp Simple Device Viewer that you can set alerts if a device goes unresponsive for a period of time.