Both Elan and Roy survived this same greatsword stabbing through multiple of their internal organs possibly including their hearts. Why would it be different for Bloodfeast? Is his HP so much lower than Elan at full hit points?
I can see a scenario where Calder kills Bloodfeast with his claws, breath weapon and magic not so much with Roy's Greatsword and even more likely that Calder dominates Bloodfeast in some way to use him against the order.