Bhishma actually died on the 10th day of the Kurukshetra war, not on the 13th, 15th, or 16th day. He had the boon of choosing the time of his death (Ichcha Mrityu) and lay on a bed of arrows for several days before choosing to die. Since none of the specific dates given (13th, 15th, 16th) are correct, 'None of the above' is the right answer.