I think a belief in an afterlife might be reached through reason. Especially in the area of mind body relations.
For example imagine your friend loses a leg. In most cases people usually think that the person is the same person with the same personality.
Someone can retain their personality through losing appendages, injury and illness.
However when someone gets dementia people will say that the person is no longer the same person. Even though they look the same. They feel their personality has gone.
This tends to be the case with brain injury and disease. Therefore, if anything, we think the person either resides in her brain or is known through behavior including language and personality. But we don't tend to identify someone with most of her body parts.
Another example is how we can recognize someone on the phone without seeing them or through reading a letter.
Therefore this suggests the body is not necessary to identify someone and a "person" may survive the decay of her body.