Is my feather duster a goner? Advice please
 

So I bought a feather duster yesterday, it was the bare worm without the tube but still had a very nice purple crown. The LFS assured me the tube would grow back-I had heard this too so I got it. It was placed into the sand substrate and appeared to be doing fine this morning-the crown was out and the worm was buried. I came home to find only 2 pieces of the worm halfway across the tank, and no crown to be seen. It appears that the pieces are still alive. One looked like it was moving and the other scrunched up when I picked it up out of the tank. The pieces appear to be the very tips-both head and tail.

Will these pieces regenerate or is this the end of him? And what would have caused this?

I have a larger electric blue legged hermit and 2 nassaurius snails as my main suspects. Other tank mates are a six-line wrasse, firefish goby, hi-fin goby, 2 astrea snails, cleaner shrimp, and small blue legged hermits.

I have moved the "head" piece to another tank with 2 false perculas and 2 small hermits.

What else can I do?

Father dusters can lose their crown when stressed or whatever.
They should grow back in time when the worm or worms now. Find a suitable place to make a new tube.

A good amount of calcium is a good start.
As the worms use calcium to build that tube.

I would remove the 2 smaller hermit crabs they are scavengers and will take any easy meal they can get their claws on.

the cleaner will also eat what's available.
I'd also worry on the 6line.

Yeah , it was wishful thinking to consider that the worm would regenerate from 2 little pieces. Both are clearly dead now-and white and fuzzy. That will be my lesson to never buy a feather duster without a tube. I imagine it would have had a chance with a protective covering-or if it had been put into isolation.

I'm a little annoyed with the LFS for giving me such poor advice. Live and learn.

Is there no 24hr guarantee? Should be able to get some kind of credit or deal on next purchase.