Right, if you don’t need the ST hub to be operational, then its losing connection with the cloud account will cause a notification to be sent. So as always, it just comes down to the details of what you need.
As for the link to the thread that discusses the V1 motion sensor, that device is no longer sold. Which is unfortunate, because it was one of the few that would send a notification when it shifted from mains power to battery power. It was very popular in 2014 for this kind of purpose. But there’s been two more generations of that device since then, and it’s really hard to find the v1 motion sensor to buy now.