Linda, that doesn't look dead to me at all. Plates are one of the hardiest LPS, and can take some serious abuse. Move it down to your sanbed or give it a little shade and wait. It'll come back out. As long as you don't see actual tissue peeling off the skeleton, it's probably just fine. From the picture, it just looks retracted. It can do that for weeks and they open back up and be fine. I had a baby plate that got pulled under a rock and burried for two weeks by my brittle star. I dug it up a few weeks ago and it looked just like that, but it's fine now. Same as it ever was.