I have a toadstool leather that did great for a couple of days in my tank. For the past couple of weeks, it has remained closed. I have moved it in the tank to an area where it receives more light and less water flow but this has not helped. Could it be dead? How can I tell? I have other corals in my tank that are flourishing: pulsing xenia, purple mushrooms, colt coral, candy cane coral and a brain coral. My water chemistry parameters are within range for a reef. I don't supplement with iodine. I do have lots of live rock and sand.
Your leather coral is not dead unless it is actually dissolving. When moving it to try and find a better location, I would err on the side of more flow. These guys really like water flow.
Have you done the standard couple of good size water changes to see if that perks it up?