Factual error: While arguable that Glass could have survived the numerous attacks upon his person (a momma grizzly, cold, hunger, starvation, etc.), his lengthy immersion in an icy river and subsequent grounding and re-warming boggles belief. While hypothermia is considered to be the cause of death in such instances, the fact is that within minutes in extremely cold water, a person becomes unable to perform the simplest of motions as the extremities shut down...and they drown. In addition, Glass hauls himself from the river and shortly thereafter is seen in his warm, dry outfit, heading out for new forms of physical and emotional abuse.
Trivia: Regarding the pursuit of Fitzgerald, the history says that Glass learned that Fitzgerald had joined the army and was stationed at Fort Atkinson, in present-day Nebraska. He traveled there as well, where Fitzgerald returned his stolen rifle. Glass reportedly spared Fitzgerald's life because of the heavy penalty for killing a soldier of the United States Army. So, there was no bloody fight as depicted in the film. No "revenge."