Hate ceases with understanding of the true nature of this world. If it would be love, it would be related to some kind of attachment via kilesa.
Anyway, if A just brings a kamma beeja (related to bad kamma done to B) to fruition with his death, then why should B establish new kamma with his kaya sankhara of killing A? Said in another way: Why should B get indebted to A now? This is my core question.