The problem they face is that Khaldoon has been laying the ground work for this for 11 years.
Graham Hunter went over it really well in his interview on 9320. In 2009 the club offered Barcelona a blank cheque and Messi wasn't interested, but they kept tabs and kept in friendly contact with Jorge Messi.
In 2012 The catalans come to City and we've got people the Messi camp know well. In 2016 when he's getting done for tax evasion (unfairly in Messi's mind) we're there reminding him he's always welcome if he feels like a change.
So obviously when 2020 comes around he knows where he's going, and the decision is made long before Ed Woodward or Agnelli pick up the phone.
It's entirely possible that if not for the decade long charm offensive that Messi would not even be thinking about leaving Barcelona. City offered him an alternative to compare Barcelona to every time he was unhappy. A club where he knows and likes the people in charge, his best friend is playing next to him, the coach who shaped his career is leading him, the executives don't fuck about in political battles.