Thanks @kraegd for the response. It looks like even when the hub is offline, the inactivity event still gets logged when you look at the hub’s events in the IDE. My thought was that a smart app in the cloud could see this event triggered and then that would fire the IFTTT action.
What I came up with, and huge thank you to @craig, was this device inactivity monitor:
I modified so that there are 2 thresholds, one for hours that an individual device has no events and the second for hours that all devices have been offline. Im going to keep an eye on the timing of normal events that come through, but for my system it looks like the largest gap is about 2 hours when nothing at all reports (temp/humidity/etc). I’ll make the system down threshold 3 hours which would then trigger my IFTTT email saying the system is down. It’s not real time like the hub itself reports out, but close enough for most of my use cases plus I also wanted a device inactivity monitor as well!