Mmm, as a sub I don't even fantasise about such serious pain, but as a Dom I can readily see the attraction of a sub that can be rebooted, so to speak, fit and well after any kind of torture.

I have written a couple of stories on those lines, but using the science-fiction idea of medical regeneration that allows you to regrow anything from skin to a new arm (or breast or whatever). A substitute body is a much more elegant way to achieve the same fantasy.