I would say that it can be used for someone who has passed on, but in the past tense.
how could you say that about him he was a human being after all.
they came upon a body, what is it? human.
being implies incarnate or a soul shrouded in flesh.
I heard a noise in the night, and demanded what form of being are you?
being, does imply a soul or life form, I would only use it in a past tense for someone who is dead.