How to maintain a z-wave network under power-outage

I’m planning on adding alarm functionality to my existing HA with Alarmo and adding a lot of z-wave alarm sensors (and ditching the old 345MHz ones).
But I want the alarm system sensors to still work in a power cut.

My questions:
Q1) Should I run TWO separate z-wave networks, one for the alarm with all battery sensors and battery backed routing nodes, and another network for the regular home automation which would power down anyway. Thus during a power cut there would not be a ‘confused’ network when 50% of the nodes go down, rather one network would be completely off, and the alarm network completely on.

Q2) What do you think to using a couple of “Z-Wave Plus Ezlo Atom USB Hub Controllers” as secondary controllers. These are basically z-wave hubs powered by USB. This way I can use USB battery backup to maintain routing paths back to the primary controller, or a PoE switch on a UPS with PoE to USB adapters. The reason to use the Ezlo Atom is that it is a cheap hub that runs on USB power, I don’t need the controller functionality, just a routing node with battery backup, and I cannot find a battery-backed routing node.

My current physical alarm is a 2GIG system using 345MHz sensors. I’ve come to the conclusion that while you can get some 345MHz sensors feeding into HA via a software defined radio and rtl_433 it will likely have some problems with supporting all my 345MHz sensors. So my plan is to use alarmo and ditch the 345MHz sensors in favor of new z-wave sensors.

Q1 It would be your choice, Most Z-Wave mesh networks benefit from the powered devices as routers to the controller. Be aware if the power does go down, the network may be slower because devices may still try to route through the dead nodes. Not sure about that nut I know non-existent zombie nodes cause this issue.

Currently, that depends. Currently I cannot recommend 700 Series Z-Wave Plus v2 controller because there is a problem in the firmware that causes network issues for large bursts of traffic. Silicon abs who currently makes all standard Z-Wave firmware is investigating.

You would also need to make sure your HA server is on some sort of battery backed up or generator power. Ideally with a UPS that can cleanly shut it down before the battery is depleted.