Dark Prince, Chaos:

Have such moves been reversed?
Yes, they have.

How long does it take?
It depends on the method of reporting the illegal move. It takes Fencer much less time (and effort) if reported to him directly via PM than if reported in the BugTracker (or at least this is what my experience tells me).

What happens if unidentified pieces become identified as a result of the illegal move?
I have no idea. Good question though. :)