Penn has said one thing crystal clear all along. Even if they agree to one of the other sites, it will be pursued on a parallel track to the development of the AD site. The site they own, which is now clear of buildings, and already has a constitutional amendment allowing a casino there.
Now, the ONLY way I could see Penn even agreeing to another site would be if the city went way out of their way to make it attractive to them (read: spend or lose money), which I think is a horrible idea.
And even then, at the end of the day, someone is paying for a campaign for the passage of the new statewide ballot to change the amendment, and it isn't going to be Penn.
ETA: all that said, Penn would be foolish not to at least feign agreement and let the city spin their wheels. At the end of the day, they simply look agreeable and will get, what I'm sure, is a better deal if it actually succeeds.