Dwarf grudges to defeat armies are aborted if you kill the faction with the last battle

xxGODLIKExx#5918

So I was playing a Grombrindal campaign and was about to finish the ancestral grudge against Naggaroth. Naggaroth has only 1 settlement left and I was at 2/3 armies defeated. I attacked the settlement. After the battle the progress was 3/3 but at the same time it said the grudge has failed because Naggaroth was destroyed and I couldn't get the master rune.

Rhox#7160

Yeah, some of the master runes rewards are missable so it counts a lot