It's important to understand it's not just the Turtle WoW people who violated Blizzard's copyrights, it's also anyone who played on Turtle WoW. They don't have licenses to use the clients, and downloading and running those clients is in violation of Blizzard's copyrights.

I wonder if Blizzard got a customer list from Turtle WoW as a result of the settlement. At the least, they could permanently ban any WoW player who also played on the pirate servers. Beyond that, they might even engage in large scale legal action, of the kind copyright trolls used in the past. "Pay us $5K and this lawsuit, which might cost you $100K plus your legal fees, will go away."

There is no customer list. The only thing Blizzard could do is ban anyone using the same IP address as someone on Turtle WoW. However since NAT is widespread in many countries and many people don’t have their own IPv4 address this would result in an extremely high number of false positives. Not to mention that multiple people could be sharing the same internet connection. Besides there’s no reason to do that. Someone who also plays on the official server is paying for a subscription. Banning that person now would just mean less revenue for Blizzard.

You don’t kill a competitor and then ban their customers from your product.