How to kill witches (The Witcher 3: Wild Hunt)

Andrei68 Did you make a bad ending?
firstly: reload the game, or load the early save, before the witch
; secondly: if you have a license, click on the game property and select the file check;
thirdly: wait for the patch, or re-install the game;
fourthly: if you installed third-party mods, delete them, and if you used the console, then nothing can be fixed.

Andrei68 The
third witch cannot be killed. She will hide, incarnating in ravens. But the HP-scale should be exactly.

TIGERblacK
maybe he makes a bad ending, there you can kill the third witch.