Soul ius a controversial idea.. Many question the body soul divide. If there is a soul we are the soul and it ceases when we expire. That the soul goes somewhere to an afterlife is an idea that came into being from our fear of death and our craving for immortality.
Science is yet to unravel the material or substance of which the soul is made of. But dead means something has left the body. When body is not robust something leaves the body and the mechanism of the body ceases to kick. I am not sure whether soul kicks the body or vice versa. Anyways men has to kick the bucket now or later!