I'm not really sure what the answers to your questions are. I didn't even have the answer I gave you above, until I was in college and was able to ask a grad-level materials chemist. His answer was, a little curt, to effect of, "That just doesn't happen." Along those lines:
Oh so at the surface the impurities make it neutral? How would that be possible? Since if I place another charged object then it would continue that crystal lattice?
Where will you get another charged surface? You not conflating a light static charge, or a current induced charge, with atomic charges, are you? Because that's not the same thing at all.
What would happen if I cut a large piece of salt in an empty vacuum and immediately place it back together. Again this has a problem as at the 2 ends of the cut parts would not be neutral at the 2 ends.
I don't know. I said that the internal faults add up to a neutral surface. Perhaps, if a crystal is split, the crystal rearranges to a neutral surface. We are at temperatures above absolute zero, so the crystal could rearrange. What do you mean by vacuum? How does that help? Or is that some sort of magic status you've just applied to the question to be cool? If we could achieve absolute zero, we might be able to saw a crystal, and then there might be exposed charges, Na
+ on one half, Cl
- on the other half. Then again, that might not occur for another reason. At any rate, we can't achieve absolute zero, so its not worth worrying about.
Like I said, I was in college, and I was still thinking, "But what if we had a diamond with only 100% pure carbon in it, and no flaws, when will it end?" But the answer was, that simply does not happen.