Probably not. I don't have the game so I cannot test this. Most likely you needed to register with an account so now it is linked to your account. And I don't think anyone is going to buy a used copy of a game, because it might not work. But if you continue to use your copy then it would be illegal, so you would defiantly have to stop using your copy.
answered Mar 19 '11 at 23:02
They would likely be able to play the campaign, but would likely have to purchase a key for any kind of online play.
answered Mar 19 '11 at 23:09