The only disappointment Darcy should really be able to guess at is that Elizabeth doesn't enjoy dancing with Mr. Collins, and perhaps that she would rather be dancing with someone else later in the evening . Apart from that, how should he know that Elizabeth even cares whether Wickham is at the ball or not? I doubt very much that he suspects she dislikes him personally! I'm pretty sure he doesn't know about her conversations with either Caroline or Jane about Wickham. He may perhaps realize that her family's gaffes embarrass her, but likely he thinks they don't embarrass her as much as they do. All in all, I don't suspect Darcy of anything but trying to say something nice when he says that he would "by no means suspend any pleasure of hers"!