Lets say that while either in infancy, during childhood, or killed in battle while he was still Temujin, Genghis Khan was killed before he could unite the Mongols and thus not create the Mongol Empire.
Now the Mongol Empire had a huge impact on history, both good and bad, but how do you think history would have changed had there been no one to unife the Mongols. Well the Mongols definately wouldn't have been unified, or least not for a while, and China would probably grow some balls and invade Mongolia to put a stop to the raids on their borders. As for other ramfications countries like Russia would probably have never formed or at least would be drastically different because the Mongols had played a huge role in creating the modern Russian nation.