I have a LTE Backhaul,but admittedly if the firewall itself craps out I would also be offline - but I can at least reboot it via a plain old GSM power plug. That thing does not directly reboot the firewall,though, but brings up a old raspberry (usb boot,I don’t trust sdcards) which then checks if outside connectivity is still available (so if the GSM power plug gets compromised it’s not an issue) and if not tries a shutdown or,if that is unsucessful, a powercut of the firewall. If that also doesn’t work it triggers a dry contact in the GSM plug which leads to the plug sending out a SMS so I know I am fucked and need to get someone with a key to the rack.