If Square wanted to sue you over this alpha leak they'd have done it already. Be mad over the fact that the alpha that got released is a horrible misrepresentation of the work you put into this project. Be mad that people betrayed you and went behind your back to release the game without permission. But you are absolutely positively not going to get sued as a result of this leak. Square has nothing to gain by suing over the alpha, because if they sued, first off, the beta would probably be leaked by someone (in for a penny, in for a pound, mirite?). They wouldn't get any money off of you because they wouldn't win (and even if they did by some travesty of justice win, you can't very well get blood from a turnip). Any "message" they'd hope to send by making an example out of you be destroyed if they lost (because precedence would be against them).
I'm not saying you should defy them, because it's not my decision to make. It's yours, and even though I don't believe the leakers put you or this site in any danger, they still went behind your back, which was wrong.