My pihole died after a couple of years, I also used it for DHCP.

Without an IP allocation, and without trying to guess, I had to factory reset my ISP router, which I couldn't access without an IP to get it to serve DHCP and DNS again.

This happened the day before I was going on holiday for 2 weeks and had given my builder the previous WiFi code so he could message me progress on the house 😂