He loves Barca, took holidays to Catalunya with his family as a kid and always dreamt of playing there.
If he's forced out by the club, he'll probably (reluctantly) leave, but you can be damn sure he'll demand his outstanding €17m of deferred wages/bonuses first. That's the holdup.
Obviously, the longer this drags on, the more likely it is that a Champions League club comes in for him and that when Barca do finally settle the deferred salary issues with him, he'll end up somewhere other than United. There's not much united can do about that, though - we just have to sit tight and wait for De Jong and Barca to sort things out.