Actually,afterlife is a matter of belief so if you believe in it and you also know approximately what life he led then you should know if he passed on succesfully.The general belief is that if there is important unfinished bussiness involving strong emotions (love,hate,etc) then the spirit will remain on this plane.(If you believe in afterlife,souls and the like).
Another option to consider is divination. Using a pendulum, Ouija board, tarot cards, scrying, etc., may have some answers. Just be aware that your own personal desires may affect the answers to questions.