I had a similar failure while I was out of the country for a month. My Raspberry Pi didn't come back after a power blink. Home Assistant, Wireguard tunnels, security cameras, Jellyfin, Syncthing backup and DNS all failed until I returned. After looking at possible solutions I ruled out buying redundant hardware because of the cost, and more importantly the time and complexity of implementing and maintaining everything.

Instead I bought a small, relatively inexpensive laptop and a router with plenty of processing power and memory. I moved my Wireguard endpoints, DHCP and DNS server to the router and everything else to the laptop and disconnected my UPS completely.

If the router is up, WG connectivity, DNS, DHCP and wifi are up. The router does reset on power failure, but my ISP has no local power backup so Internet is out until power is restored anyway.

This laptop loafs along at 10 watts and costs about $2 per month to operate despite our high electric rates. My old UPS drew 75 watts most of the time even when there was nothing plugged in and cost more than $16/month to run. The laptop's battery is firmware limited to a 70% charge so the battery will last years without degrading and making other battery issues unlikely. It provides 7 hours of operation if power fails compared to an optimistic 20 minutes for the UPS. Power blinks (and there have been plenty) have no effect on the laptop at all.

I've been happy with this configuration. It has worked flawlessly for almost 2 years.