If Charlotte had survived, and had borne surviving children, the UK and Europe would look very different today. So would much of the rest of the world. Leopold wouldn't have been chosen as King of the Belgians, so Belgium and Luxembourg would have been different. So would the Austro-Hungarian Empire. Parts of Africa wouldn't have become Leopold II's personal fortune-makers (and horror-makers as a result of his basically enslaving and brutalizing the population) since he wouldn't have existed. There would have been no Stephanie of Belgium for Rudolf of Austria to marry either, so he might have married someone else and had a son instead of a daughter. And so on.