Both player seems to be made for each other, imagine how the world will react if there is only one of them. IT will be very boring to see them playing like it is a training game and both player makes each other compete more for the fame, they probably wont be playing at their fullest when they have no rival
And if we look World Championship 2014, Messi was only one person from Argentina who tried everything lonely to be argentina in final but yes, he wasn't lucky enough because Argentina lost chance of win, it's horrible when you try everything lonely and in final you lost.