Think ot more like a cold sweet. You get stressed out you can have cold sweets. With shrimp, crabs and other inverts they can and often do with rapid changes in SC, Temp, being introduced to a new tank, ect... Now most of them do leave the molted shell in plain sight to distract fish and others who might eat him/her. My cleaner shrimp molted the next day, after I bought him. He was a bit stredded out being a new tank. I thought he was dead but I took a closer look and it was only his shell. I looked around my tank and after about 10 minutes I found him hiding. I have had him for about a year/year and a half maybe. Hes bold unlike all my crabs...
Now also keep in mind, I have a few crabs in my tank emralds and others. After I put them in the tank then for the most part they dissapeard. I know there not dead, being I find and see them from time to time when I move things around. Most mostly they hide in my rocks and sand, or anywhere they want. I had one living under a colony of zoo's fo a long time. Hes still there, but I never see him come out on a normal basis. So keep that in mind most crabs hide and you might not see them for months at a time if ever unless you stumble apon hem while move a rock or something else.
So to keep this short as possible it happens. He might e dead that I do not know, or he just molted and is in hiding only time will tell.