Not to rain on your parade, but when I went on the tour earlier this year (and I highly recommend going on one, it was very interesting) they said that they can and will cancel tours at any time for diplomatic reasons. With the current tensions, who knows if they are doing tours into the actual DMZ. I'm sure you can still visit the 3rd tunnel and Dorasan station, etc, though, all of which are just outside of the DMZ proper.