An extent is a binary segment of the virtual hard disk. (What you called slices.)
More often than not by the time one is prompted to perform a repair it is often to late at that point and then with the reboot it probably killed it for good. That said, I'd have to examine the disk myself to determine whether not it could be salvaged. If it can be determined which extent is corrupt sometimes one extent can be swapped for the other in an attempt just to mount the disk for data recovery not necessarily have a usable OS again.
Sent from iPhone.