The bad guys that have this debit card data are not going to attack online merchants for goods that they will have to convert to cash. They have been walking straight to the ATMs for the green dollar.
Fraud Protection on the long term
The impact on merchants in the CNP world will be minimal; certainly no more than a few numbers of credit cards but probably less. I do not think the CP merchants will feel it much either. Consumers, on the other hand, are going to take a huge hit. As you probably know, credit card holder's liability is limited to $50 under FTC regulations but I do not think there is any such limit for debit cards. The card holder is responsible for keeping the PIN private and shame on him if it gets out and he does not report the card stolen.