Live: It's a crappy law, but that is the law. I don't think you get a fine, but the cops will insist that you let the person back in. Similarly, she cannot put his stuff outside to get him out. Again, if he calls the cops, he gets to move it right back in. I think this is largely because of rent stabilized apartments in NY.
My friend ended up paying the rest of her lease because her xah did not have a job to pay the rent. Had she not paid, the landlord could have gone after her legally for the money. So, she paid because he refused to leave and he ended up having to leave anyway. That is why people are so weird about letting people stay with them in NYC. More than 30 days, you have to evict them. That could take up to 6 months here.