I don't have a clue how this site is set up, from an IT perspective, however I do know that the old DB likely still exists. In my experience, usually the old DB is ported into the new site prior to activation or it will overwrite the new DB which I'm pretty sure nobody wants to do.
That said, I wager a separate access point could be established to the old DB for the PMs (which are usually indexed separately), and possibly a few posts of value could be placed into an archive for reference.
These are painstaking "housekeeping" chores for system admins and can be very time consuming.
My best guess is that the appropriate people will consider doing something with the old accumulated data once the massive job of making the new site reliable and bullletproof is complete. Patience should be the order of the day for this as I would think that much of the stuff in the old DB isn't worth bringing into the new one. This is a fresh start as far as I am concerned and I am extremely impressed with the great effort made by the entire staff.