The film only has two rescue parties coming to the Donner/Reed families. In truth, it took four relief missions to get the last of the survivors out, starting from February to April 1847. The fourth, and last, mission found just one man, Louis Keseberg, alive. He was found in a cabin surrounded by the bones of people. He survived and became a pariah of society.
Only one time is cannibalism mentioned, when Mrs. Reed comforts a dying Milt Eliot. The Donner Party fiasco gained its notoriety when many members, but not all, resorted to cannibalizing their dead friends and family to survive the winter. This includes the body of Milt Eliot being consumed, perhaps by the Murphy Family.