The Archaeology of the Donner Party (2005) edited by Don Hardesty is an excellent treatment of the Donner party. Every indication strongly points toward cannibalism as a final act of desperation of the group. Later, a few survivors insisted they did not engage in cannibalism. A recent limited excavation failed to find human remains and there was some publicity from that effort, suggesting that the failure to find human remains meant that cannibalism did not occur - but that was a bit of backward, flawed logic. People died and people were eaten. It is the harsh reality of the situation.