yes, it’s body will take a long time to regenerate.
I have no idea “where” it is regenerating at; I suppose if I did, I could go and kill it again every few decades to keep it from coming back.
The only way I can think of, off the top of my head would be a Cloud of Disintegration cast in the Abyss. I “think” that would do it, but I won’t bet my immortality on it.
Tizzy