Tissue, generally grows back, as its usually fat or skin. Sometimes it doesn't though depends on diet. Like my left wrist, I dislocated it and had surgery and cast on it, a year or so ago. To this day, when I flex my left arm, you can see the cannon between the two bones/muscles in my lower forearm. The fat went bye bye and didn't come back. One way to tell is to flex or see how big your ankle is compared to the other one. If it's a bit smaller it probably didn't come back, but you don't need it, unless your going to walk a long time in the cold or something.
Kit