I think my PiHole is up for 3+ years on a Raspberry Pi dedicated to that task. Did not fail once since then, so not sure if "DNS is going down" is really an issue. But maybe I've got survivorship bias.
Living in a North American city with power wires being above ground, I have had so many power outages in the last five year, it was kind of a crazy thing to get used to. My Pi would not deal well with power outages when running through the SD card and so I stopped using it.
I've had a raspberry pi and pihole going on the same SD card for approximately seven years now.
I also regularly reboot the pi by simply cycling power.
The solution was fairly simple. Send the linux log files to /dev/null (or whatever it is actually called, i.e. RAM) and disable query logging in pihole.
I ran it on an old laptop and never had issues. The extra ram and cpu + actual disk hd gave me ~99% uptime even after power outage no sd card corruption. Laptop auto rebooted on crash too.
I live in Vancouver BC, we have a power outage every 1-2 years due to high winds or fallen power poles. I noticed some devices on my home network whilst connected to power have power quality issues too, no doubt a UPS would help here.
