Many were burnt to the ground. General Sherman, in his "March to the Sea" destroyed by fire as he went.
But a few lucky ones survived, usually because they were of some use to the Yankees during the war. With courage and perseverance, they made it through the difficult "post war" days as well, and some are still thriving today.
A couple of examples in Georgia: The Burge Plantation survived, is now a private hunting club and an organic farm ... The Gaither Plantation, also in Georgia, made it through too. These plantations are described here: http://gocovington.com/destinations-events/destinations/