You can sacrifice anyone without needing affinity with Gro-Goroth in the intro and thereby aquire bloodmagic.
Though if you don't want to sacrifice anyone, and you only want necromancy you can start as Marina and choose blood magic as your specialty.
You also simply do not see the power of Black Kalev. He casually kills even powerful opponents with a single strike and will only make the most optimal of attacks during a battle, without needing any player input. No wonder he leaves your party when you consider him to be worst than ghouls.