I think nobody does know, because it's probably never happened. It would take at least 1-2 years. It could be possible if one man begins, he gives his game to his son, that son gives it to his son etc.. But it would take a VERY LONG TIME! Also, once you don't have any other empires around, you won't be able to fight, trade, socialize, talk, or take missions, and the game would suddenly suck.