Rikh wrote:i would assume one part of the body would die
Either the head disappears and another one pops on the body, or the body disappears and it pops onto the head
Although Berserker is more along the lines of high speed regeneration. He's like a person with the worlds best (actually much greater...) immune system
Will berserker come back to life after suffering a fatal disease? .... I guess God Hand would prevent future deaths from it. nvm
We need a Servant that attacks with terminal diseases
According to the translation, little pieces of Berserker's brain and spinal fluid splatter Shirou and co., so I'd say his head was done for, with an huge hole on it in the very least, if not pretty much gone. So he can restore his head: why didn't his arm regrow is a good question... maybe he needed to die once before restoring it with God Hand's boost, or maybe non-fatal injuries are just ignored by God Hand, and thus he would have to rely on his normal regeneration ability as a Servant (picking his arm up, reattaching it, etc).
Something I'd like to add is this: the same that Avalon's healing powers are more along the lines of restoration than regeneration (stated ingame), Berserker's God Hand seems to work like an automatic restoration that, upon death, restores the body to the previous state just before being killed, and thus avoiding effects such as, y'know, dissappearing in little sparks and all that. Thus, cosmetic things like a lost arm or a burnt face may be left to regenerate by themselves (Servant ability), instead putting priority on reversing the cause of death and only that. So, if you blow Berserker's head most of it would have to be restored in order to Berserker to be alive, but if it's a huge injury to the chest reaching the heart (something along the lines of what Gae Bolg would do) the restoration may just restore the hearth and leave the broken ribs, open wound and everything for the slow, time consuming regeneration. And let's not forget that regeneration in Fate seems to close wounds first and fix the insides later...