You are asking a key question no Christian has asked before, as they expect bodies to be reassembled after Judgment although the molecules were scattered at death and might exist in worm or crows! There is no clear teaching of a soul in Christendom. The implication of any mention of soul has been that the body is implicit. But if the soul is separable from the body, Christianity falls away as ridiculous. If only spirit is real, placed upon a physical platform, then the best thing to do with dead bodies is not cremation, that adds to global warming, but simple burial in the woods with a wooden marker that future generations may care to renew depending on the value of the individual in his or her contribution to global joy or harmony. And that next person, who is the same person, can even visit that gravesite, rejoicing that the body has been made new through God’s dispensation. If you are old there is lamentation the body is falling away from weakness. But half of all our lives are spent old, and the young ones keep arising, rejoicing by God.
