The identity of their entire (sad) fanbase is that their team plays in NYC. Unless the MLS or the Yanks makes them leave Yankee Stadium for a real soccer venue, I can't see them moving until they find something in one of the boroughs. I don't see Garber forcing the issue, but maybe the Yanks would at some point.
It would be fucking hilarious if it did happen.
The Yankees will want them to leave and leave soon. The team did what they wanted it to do. This is the history of the Yankees.
They started a television channel. All they had was the Yankees and Yankees replays. They tried to fill in airtime with some dopey shows like Center Stage and Steiner Sports. To fill in further, they purchased the Nets and Devils. The Nets immediately signed a deal with YES Network to fill in winter time. They ended up reviewing the contract that the Devils had and it didn't make sense. They also didn't have the spill over channel to show the games live in case the Devils and Nets were playing at the same time. The Devils had lower ratings and they did take in some money from MSG, so they stayed.
After locking in the Nets long term at a nice snazzy price, the Nets and Devils were sold off. The teams weren't purchased to make their brand stronger and better. They were purchased to help fill in their channel lineup on the cheap.
NYCFC is the same. They just finished building Yankee stadium. They want to gain income on a property they're paying on. Also, you can fill in some weekend daytime hours programming with live sports as opposed to replays of Arsenal or ManCity.
I think Yankees ownership and management were hoping for a maximum of 5 years of owning. They won't give a shit where the stadium is. The second a deal is struck on stadium grounds, The Yankees will sell off their share in the team. They'll retain television rights though...