I think it's all fantasy talk, we've heard it all before of players saying they'd like to finish their career in such-and-such a place (Tevez at Boca Juniors, etc.).
Look at Barca's central midfield options:
Xavi (32)
Keita (32)
Iniesta (27)
Mascherano (27)
Fabregas (25)
Busquets (23)
Thiago (21)
Their midfield has so much talent that Mascherano plays in defence now and Fabregas has started about 15 games from the bench this season.
By the time Yaya's contract expires he will be 32 and only Keita from that list will be guaranteed to have left the club (Xavi will play until his late 30s, IMO) and they probably will have signed or produced another player or two by then, leaving little room for a returning Yaya on big wages.