Hard to say, especially with all that blue light in the photo.
Over the years (like the last 6) I've lost a few RFAs (I have 40+ at the moment) for unknown reasons.
If it is still firmly attached to the rock and the rock is too big to take out of the tank, I'd leave it and watch. If you can get it out and put it in a smaller container, that might be a good idea. A healthy RFA can survive for weeks in a small container if you just do a water change 2 or 3 times a day. If it dies and falls apart, it doesn't do any real harm to the tank. I just lost one in a 16g breeding tank and all the other RFAs, shrimp and crabs seem to be just fine.