The Fall as it will become known, is the collapse of the human kingdom and the apparent death of the royal line, brought about by the Shadows and the Orcs of Zord. The Orcs of God take advantage of the collapse but are not really interested in wiping out the humans, but rather converting them or enslaving them.
The only bastion of the human kingdom that survives will be the city of Folkist, but that will be under blockade for over a year initially so isnt an option for the players to begin with.
The options open to the players are to flee to one of the other races, north to the Centaurs, north east to the elves, east to the faeries and south east to the dwarves. None of these are a very attractive option due to degrees of hostility that the late King Nagrom (under Shadow possession) had cultivated.
The players, fleeing Castle Bord, will be presented with the option of going the the Forest of Anduin (faeries) simply for the reason that orcs will not enter it due to racial fears of faeries. Once there they will need to befriend the faeries. The fleeing masses of human refugees will start building up in Anduin and eventually the humans will move to the hills south of Anduin and establish a new community.
The players will be involved in all of this to some degree, establishing them as leaders in the new community.
After the initial successes the orcs will grow less organsied as the Shadow leadership turns to other events, which will allow the humans to begin to recover. Further the two orc groups will slowly grow antagonistic toward each other as they gain greater proximity, and eventually begin fighting each other.
The players roles will be to hold the new community together, and to lead it into recovery. At the same time they will need to pursue the various quests open to them and to forge alliances with the other races.