The wizard is shocked by Durg's words. He glances at Semabin for confirmation. He then sits down on his couch without a word, and doesn't speak for several minutes. If the PCs say anything, he raises his hand dismissively. He nods occationally as he thinks to himself.
"Yes. As may be." He says finally. "This is not totally a surprise. Thank you for...er.... Let's see here. The reward was explicitly for returning my daughter to me. You have not done this. Therefore, I am not bound to pay you anything more. You have already received a fair bit of coin from me. However, I do appreciate your services, and I would be willing to give you additional compensation, on one condition. If you will be silent on the results of your inquiry, and simply state that you provided a private service for me if asked. I will give you each a 100 gp ruby. In either case, you may depart."