Well I would have responded directly to the ethics of euthanasia but you based your question on the non existent of the afterlife as a reason to reject the ethics of euthanasia. To that effect I would simply respond (as some philosophers have done) that reality is bigger than our minds. That you are oblivious of a small town called montepaone in southern Italy does not mean that such entity does not exist. Regards!
In my opinion, the afterlife either is unknown or no, someone must live and know this life at first where the euthanasia has not any position, existence and ethics.