In my experience a fish is not the most likely cause for eating this type of polyp. Picking at yes but not eating. But it could happen. The problem is purple death is a paly and it will have what is know as palytoxin. That is one of the most toxic substance in the ocean. So it is not very likely to have been eaten by a fish. All paly have the toxin in them just at different levels. If it did eat it, it would show signs of being sick or dead for the majority of fish. Not many fish can or want to eat them. A few will but not very many, typically it will be the specialized feeders like a file fish that will risk it. That is because they can use it in their tissue. Most people don't keep these specialized feeders in the reef tank. Hence why the palyis are so toxic.
With that being said a grazer could have bitten onto the polyps and spit it back out while cleaning off the rock. So I would look in the corners of your tank for any loose polyps. That bird wrasse is not considered reef compatible. Out of any fish I would look to that fish. Some Foxface have been known to pick on corals but I don’t think in this case it would swallow the polyps willingly.
There are many reason for the polyps to be gone quickly. Bacterial infection, shrimp, nudibranch, newly glued frag plugs. That haven't had time for the polyps to attach to yet and they let go. These are some of the more common causes.