Its been my experience that excessive tissue reccession like in the pic you provided seldom is reversable. It may pull thru but I wouldn't bet on it. It may be worth the attempt...insure it has adaquate lighting...in its condition I'd avoid excessive current...and if it'll respond try a direct feeding of small particle sized meaty type foods...best of luck and let us know if it makes it.
Don't take it out of your tank if it appears dead. Occasionally plate corals receed ubntil they appear dead, and then start budding new plates. No guarantee, but worth a try.