They would not be giving up anything in JFK. They would only move terminals. The exact same flights would operate. Delta has tried to get terminal 8 within the last few years and they have port authority support since AMR can't utilize all the gates in 8 with the restrictions on flights out of JFK. The port authority is now a creditor of AMR.
Miami is profitable and would command a lot of cash. Cash always talks especially to creditors. That is why you don't want to go into chapter 11 if you can avoid it. AMR management is now in a bad place. They have a viable offer from USAIR. Even if they fend it off they are now going to lose most of the hoped for gains in chapter 11. Regardless of how it turns out and who retains control the labor agreements with the unions at AMR is a very crafty move on the part of Parker. He either gets the airline or they emerge from Chapter 11 as a standalone but don't get to rape the employees and creditors and lose most of not all the benefits of filing in the first place.