Is there a possibility to kill the madman myself?
During the quest "Reason of State"
the mad king Radovid gets killed
by Philippa Eilhart.
Is it possible to kill him myself? Or might there be a possibility that any other NPC gets the killing blow? (Vernon Roche or Ves for example)
No, unfortunately, the killing blow will always be given by Philippa. Well, she deserves the right to do it :)