For the most part if you have any live rock in your tank you have pods. Because you also have fish you probably won't see them without a flashlight a couple hours after the lights go out. Not only do the fish eat them, but when fish are around pods get quite sneaky. Instead of digging around in the open without fish around, they start scurrying around hardly noticed. Take my nano for instance... Before I added a fish I had thousands of them in plain view; and in the past month since adding the fish I've seen two very briefly. Keep in mind this is a five gallon tank, so it's hard to miss anything.
It's hard to tell why Mandarins don't usually make it after being starved. It's possible that they develop an opportunistic parasitic infection, but it may be for other reasons as well. It could be that their digestive system simply shuts down after such a long period with nothing to digest. That happens with a lot of animals. It could also be that their appetite is gone, as also happens to other animals after starvation. For whatever reason though these fish usually don't make it. We have an LPS (Wild Side) that always stocks a load of Mandarins. I hate to see it, because you know most of them will soon meet their untimely death.
Clayton