On the tenth day of the war, Arjuna killed Bhisma using Shikhandi as a shield. Bhisma would not shoot at Shikhandi, because of her being a woman! He himself revealed to the Pandavas the way to kill him. He had ‘Ichhamrityu’, so lived another six months on his bed of arrows waiting for ‘Uttarayana’.
Why arrows were not removed from Bheesma’s body?
Arjuna released a volley of arrows. Hundreds of arrows punctured every limb of Bhisma’s body, his hands, his legs, his trunk, his thighs, till the grandsire fell like a giant Banyan tree in the middle of a forest. It is said that the earth would not accept him for he had lived too long – over four generations instead of just two. It is said the sky would not accept him because he had not fathered children and repaid his debt to ancestors.
While Arjuna was pouring his arrows, Bheesma had cried
My son, the earth will not accept my body, for I am too heavy for her lap. The skies will not accept me, since I have not produced children and have committed a sin. Now that you are on your path to Dharma, do mercy to my withered body in such a way that I belong neither to the earth nor to the sky.
So he remained suspended mid-air by Arjuna’s arrows.