Bold move, attempting an in-place upgrade on a domain controller that was also serving DHCP. Crazy.
YOLO, I guess.
Time to seize roles on another DC and call it a day on this one. Either recreate DHCP or attempt to grab the DHCP database offline and copy it over somewhere functional. I’ve had to do this before in cleaning up someone else’s screw-up.
This is the kinda crap I used to have to deal with routinely.