The body after a person dies is burnt and the soul dissolves into the universal consciousness. But this dissolution of the soul does not happen right after a person dies. But according to their Karma, the soul travels the path of pains and sorrows to ultimately dissolve into the universal consciousness and they do not exist anymore.
This path of dissolution is also different for every soul, for some there is tremendous pain inflicted for moment and they dissolve, but for some there is little pain for a longer duration. This is also true for the religions where they have other ways to dispose the body, like burial. The person’s belief system has nothing to do about how a dead body will be disposed, but it depends on their karma during their life time. Even if the person is buried, but there karma is more amenable to the fire element, their bodies will accepted by fire. Burning and cremating are only the visible spectacle, whereas the disposition is a spiritual process.
After the disposition, nobody can contact them and they have been stripped of everything they have, their names and identities, their Karma, their knowledge and experiences and everything they have accumulated in their lives and their soul becomes a part of the consciousness of the universe.
Everything that we consume is a loan from this universe starting with knowledge, five elements, things that we eat and every other thing, and at the end all these things returns and dissolves into their respective elements. And the person does not exist anymore this is one aspect of looking at it but there is another aspect as well, even if the person has died he does not have his own body, but he can contact people by momentarily taking body of another person for a small durations. This is the reason why we discover things by reading, writing, talking, and other forms of human interactions. Certain aspect of communication generally generates thoughts in our mind which are nothing but communications from the souls from other dimensions.
Right from our birth we are running nowhere but only towards our death, and Hindu Yogis only expedite this process by their practices to complete process of dissolution, while living inside this body and they live on the threshold of life and death. And when the time of their exit arrives they leave the body with minimal pain and enter the state of eternal bliss by dissolution of the soul in the universal consciousness.