I would bet that it will grow a new crown. The first feather duster I got did the same thing about a week after I put it in the tank (I have 5 now all doing great
). I left it alone and about 3 or 4 weeks later he was back to normal. Seahorse Fanatic posted that the new crown will be smaller but that is not the case with mine, actually I think it ended up being a bit bigger. Might have to do with the type of feather duster it is though. This one's crown is mostly brown with a bit of yellow.
HTH