What I think will happen is:
Barca will agree a fee with United - apparently done.
Barca will tell de Jong its pay cut or leave - also done apparently
Barca will offer de Jong a take it or leave it offer, one they KNOW he won't take, it'd be the absolute max they can legally cut his wages by, and writing off his deferred wages or cutting them big time
De Jong will refuse the offer and Barca will flat out tell him that he has no future at the club. His only option is to leave.
De Jong will reluctantly leave and Barca will spin it as they tried their best to keep him and offered him a deal that they believe was modest and acceptable. They'll paint him as a mercenary who cared more for money then the club.
This will all play out over the next few days in my opinion