All you have to do to unlock it permanently is earn 10 First Wins of the Day in Unranked or Versus A.I.
The original Wings of Liberty campaign.Here is a specific rundown of everything that will be available to you for free:
ORIGINAL STARCRAFT FOR FREE FREE
Starting November 14, you’ll have free access to the original Wings of Liberty single-player campaign and every Co-op Commander, and will be able to unlock access to StarCraft II’s competitive multiplayer content for free. Curious what that actually means? We know “free-to-play” can mean a lot of things for different games, but we’re here to assure you that when we say that we’re making StarCraft II free-to-play, we really mean it. We recognize that you might have found your way here after hearing the news that StarCraft II is going free-to-play very soon-on November 14, to be exact.