i wouldn't take this particular offer too seriously. still, i think it's likely that xavi will join another club before he retires. he has won everything and more with barca and spain and his name is a byword for the most successful spanish football generation and its style. so judging by that, what perspectives in terms of new goals and experiences does he have at barcelona? we cannot see inside his soul and know for sure, but the way i judge his character (and one of the reasons why i really adore this guy), he would be eager to play some football in another environement, not necessarily for the titles, but for the fact that he would have missed out on something if he retired without doing so. look at raul, he's really enjoying himself at schalke, and I'm sure he will consider his time at germany one of the best parts of his career even it was a "downgrade" in comparison to real.
and of course, the point could be made that if xavi plans to be a manager one day, having first hand experience from other countries and their style of play is certainly a bonus.
that being said, the day when the 6 of barca is not named xavi hernandez will be a sad day indeed