The subtext of the question does a good job in identifying the particular moments where Eliezer's faith in God is questioned and eventually negated.  It is a process by which Eliezer undergoes a systematic erosion of faith in God based on his experiences.  The idea of being taken and herded in the train causes questioning, but with a reassurance that "there is a plan" and God's motives have not been fully revealed.  When Eliezer arrives in Auschwitz with the poem "Never Shall I Forget," the full weight of his anger towards God can be felt.  When Eliezer says, "God is hanging on the gallows," in reference to the death of the child, it is a moment where Eliezer believes God to be dead.  Finally, I think that when Eliezer says that "Hitler kept all of his promises," it is akin to a  repudiation of God's presence in Eliezer's life.  The abdication of faith is brought about by Eliezer's experiences.  At the end, Eliezer is shown to be an individual who still probably believes in God, but has endured so much that the relationship between devotee and divinity is a frayed one.  In bringing this to light, Wiesel's work becomes a philosophical tract where individuals are compelled to question the nature of divinity in a context such as the Holocaust.  There can be no simple answers in this examination.  This is where Wiesel's work brings out a level of questioning that is more of a discussion than anything else.  There is little certainty featured here, but rather one that explores the complexity of both religious faith and the losing of it in the face of unspeakable cruelty and horror.