This is the biggest shocker. Blocking someone removes the friendship. You are essentially starting from scratch. If you want to see their posts in your News Feed again, you must send them a new friend request.
Good news for the non-confrontational folks. Facebook does send an alert saying, "Hey, Jane unblocked you!" However, they might figure it out if they suddenly see your comments or if you pop up in their "People You May Know" list. how do i unblock a person on facebook
However, there are specific rules regarding friend requests and blocking timeframes that you need to know. This is the biggest shocker