Just....set up two RPIs with Pihole instead of one? Chances are your router can have a fallback DNS. Sure, you have to update the rules in both places, but honestly it's not a big deal, and you now have redudancy.

I'm running 2 powerdns recursors and authoritative servers, and 2 piholes (long story why so many), and none of them have failed on me so far, and when I took one of them offline, I didn't notice anything because the other took over. And if anything REALLY fails, I'll just switch my router back to using cloudflare or Google or quad9 temporarily, and at least Internet access will be restored so people can at least browse the internet.

Pihole also has an API and a home Assistant integration, so you can create an AdBlock toggle switch for others, in case it blocks something and they need immediate access. Not ideal, but it's a doable workaround.

This is really something that's super easy to self host, and mitigate if something goes wrong. Especially since that commercial router is already a single point of failure for most households.