[quote=IVIasterJay]
If part of one is cut off, like a limb or their head, and is put back before they regrow that piece, would the piece reattach?
[/quote]

Depends on how long its been separated. If it was very recently the two pieces would work together to re-attach. If it's already been quite a while, it will grow a new one instead of re-attaching and the old one becomes a discarded body part with no function other than to rot in the streets.