Messi and Ronaldo are not irreplaceable. Barcelona/Real Madrid could bring in Hazard or Gotze and not miss a trick (aside from probably 20 fewer goals a season, which means they'll have to settle for fewer 5-0 wins and more 3-0 wins). There will never be another Didier Drogba for Chelsea FC or the world, though. The man deserves more than a statue, he deserves a monument, an epic poem even.