If there will be major buildings built, and major quest sistem, there should be events (with a report to the player) like Minath Tirith's siege, and if the player isn't there, the event doesn't begin, and if a major building will be ruined, there will be builder npcs to repair it (for extremely much coins, of course) or keep it ruined (If the player is the enemy of the building". And if there is a fortress, there should be other type of invasion, with siege weapons and a chance to change it into an enemy building, like Minas Morgul.