I had a few snails that appeared to be dead. But before getting rid of them I took them out of the tank and placed them in a teacup with some tank water and food. I placed the snails in a circle with the food in the middle. Turns out a couple did eventually move so I kept these and discarded the rest. So sometimes they appear dead but are just sluggish for some reason.
I was so hoping your snail would make it. I have a silly snail that I just love, ugly pitted shell with a fissure that has healed, algae growing on her shell. I worry and fuss over her and just love her.