Chip and Pin would prevent none of the leaks, it would prevent the usage of the stolen card numbers after the fact.
The chip is not part of the equation for online transactions. So if everything but the chip is stolen, the bad guys are going to use the card online.
Check out http://krebsonsecurity.com/2014/05/the-target-breach-by-the-..., particularly his "by the numbers" section:
0 – The number of customer cards that Chip-and-PIN-enabled terminals would have been able to stop the bad guys from stealing had Target put the technology in place prior to the breach (without end-to-end encryption of card data, the card numbers and expiration dates can still be stolen and used in online transactions).
With regards to online use, I'll say I'm not familiar with how Chip and Pin really works, but presumably they have some guard for online use, right? Or is that just wide open still?
How would having a having the Chip and Pin have prevented the data from being stolen? It does not. The "Chip and Pin" argument is brought up each time this sort of retail breach happens, like a reflex.
It seems that this is not that same type of system or am I mistaken in some way? Seems to me that it would have helped; my account number/card number/exp. date are useless on their own.