All this talk and speculation of why he left at that age is irrelevant, it was a decade a go and he's back now, and most of this is hearsay and we will never know the truth so no point basing conclusions on that.
Looking at Cesc now, he still needs to learn a lot about leadership and generally about carrying himself on the pitch before we can rely on him as much as we do with Xavi and Iniesta. I dunno, I may be talking shit but I often get a feeling that he doesn't really try hard enough and doesn't sacrifice himself for the team as much as say Busquets. He was poor in the first leg of CDR vs Madrid, but after grabbing that goal (which Messi created) his performance was a lot more relaxed and lacked intensity, maybe he thought he's done his bit by scoring that goal (He and Pedro's criminal misses cost is the cup). This is subjective, but I don't like his attitude based on what I see. I'm willing to let somebody who has a bad game (Alexis/Pedro) off the hook because they usually try so hard and their attitude is admirable. Can't say the same for Cesc. He has a lot more to learn technically as we've all discussed on numerous occasions in this thread, just look at Messi's 2nd and Villa's goals and just how quickly Iniesta and Xavi executed their passes respectively after dispossessing the opposition, Cesc usually ponders when he should execute the pass (do not confuse pondering with patience here, assuming he has pressed Milan as hard as Xaviesta to steal the ball anyway). He slows down the attack as he needs a lot more time to moe the ball than Iniesta. Having said all this, it's better to have him than not, given the number of games we play and Xavi(age) and Iniesta's injuries, and his creativity and willingness to attack makes him an asset, but in do or die situations we can't expect him to do what Xavi or Iniesta do. I'm still confident Tito will find a place for him in the squad without sacrificing our overall performance (as he already did so far this season).
Bestikas, you're forgetting that Pique left Barca for Man United. The main reason why he returned was that Ferguson chose Evans over him, and sat him in the stands for their CL final. Why have you not mentioned him at all?
Now that you mention it, their performances have been strikingly similar in the past couple of seasons, unfocused and lethargic