Thanks mate. It was a bit of a rabbit hole, I found stuff about the watchdog package, and you can configure it to use the iTCO_wdt module, but I also read it was blacklisted, and then I just gave up.
I posted somewhere else in the thread what lead up to the hang. And, I think I'll buy a WiFi smartplug so I can remotely reboot everything; assuming the WiFi still works :D