If Barcelona had bought Cesc, they would be stronger to win a Champions League. However, in another point of view, with the permanence of Cesc makes Arsenal stronger. Concluding, I prefer that Cesc stays at Arsenal.
x2 Dzeko or Vucinic in Chelsea would be great. If Chelsea don't sell any player, they just need to buy a Attacking Midfielder Center. However on the next season, a forward and a back center must be bought.