Since he did it out of stress.. I would just leave things be with him as much as possible- return the decoration but make sure it's secure. Want to get him to where he is comfortable and stress free so he won't continue this bad habit. Once they get into tail biting, it's very hard to stop them. I have a VT that will take a chunk out now and again.. he started due to stress (he's a momma's boy, at my desk and when I was gone for surgery he was alone and no one to play with- he started tail biting at that time) Even though things are back to normal, I'm around and he has new neighbors.. he still doesn't fully stop. Grr.. (going to have surgery again soon.. I'm going to put him next to the bed for that one lol)
So if it's optional- return what you removed and make it safe.. sometimes they get attached to objects in their tanks- I have a couple that must have their cave/cup or they stress out if removed. Hopefully with the return of it, and just a calm setting for the next few days he will stop chomping.