We let Beletti go for a reason - he had done an honourable duty, but he was too old to play a major role in the team. He won't come back cause his Barca career is over, he finished on a high, why would you want to go down from there? He's a club legend to a large extent; if he were to come back it would be irrational. It would be like bringing Sylvinho back to play.
Belletti will always be the man, for me, who won us the Champions League final in 2006, and won us the Champions League semi-final in 2009, when he came on as a substitute, scuffed a 1-on-1 (to me it was clear he did it on purpose), which gave Barca the opportunity to counter-attack, and from that counter Iniesta scored the winning goal.