Ronaldo is next to impossible to replace. Messi will be too once he's done. Xavi and Iniesta were my favorite players on Barca and they are also next to impossible to replace. I just think the imbalance in the favor of these teams has been broken a little since some of these icons left and Messi can't do everything himself. Also, you'll notice if players get enough money they may be fine staying put. I hardly ever hear Man City players linked with leaving for example.