Just think of the megalania that existed during the last period of extensive glaciation. They were huge furry mammals living in very cold habitats, so cold that as things began to shift towards warmer temps species died of as their food sources did. Sasquatch may well be the megafauna primate/hominim, evolving right along with the rest of the giant mammals that came to be, only their cooperative behaviors(hunting, defense, food gathering) higher cognition, and omnivorous diet, allowed them to adapt better to the changing conditions, and survive to this day. In that regard, things are probably almost balmy compared to the glacial days.