What keeps Eliezer going during the brutal march? How does his link to his father affect his will to survive?

The thought of losing his father is of utmost importance in Elie's mind during the disastrous march from Buna to Birkenau. The prisoners are forced to essentially run 42 miles in the freezing snow, urged on by the SS who would shoot men who could not keep up with the pace. Others that were too weak were simply trampled. Elie remarks that the SS troops were often changed so they could rest, but there was no rest for the prisoners who feared being trampled by the desperate men behind them. At one point, Elie contemplates death and giving up. He thinks it would be easy to just drop away from the mob and die in the snow. He says,

Death wrapped itself around me till I was stifled. It stuck to me. I felt that I could touch it. The idea of dying, of no longer being, began to fascinate me. Not to exist any longer. Not to feel the horrible pains in my foot. Not to feel anything...

Elie's will to survive is based on his obsession with taking care of his father. He believes he has no right to die because his death would directly lead to his father's death. He says,

My father's presence was the only thing that stopped me....What would he do without me? I was his only support.

A little later when the prisoners are resting in an abandoned brick factory, Elie remembers seeing the son of Rabbi Eliahou attempting to distance himself from his father. The boy had obviously grown weary looking out for his father and hoped the old man might die so the burden would be gone. Elie very much understands the boy's thoughts, but Elie never gives up and stays with his father until the bitter end at Birkenau.