When NWN 1.69 is released and HG upgrades, CEP 2.1 will be required to play Higher Ground.
With this in mind me thinks it will be a bit before we even see it going into HG. I'm sure the DM team have to make sure all their ducks are in a row. Then they will give the exact instructions that will be needed before they want us to download different things for HG.
Also Worldgate set up by Acaos will help alot in making the transition found here when it's time to switch.
the critical rebuild patch so far has never needed any of the old files to be present.
When you go to update to 1.69 it will abort the update if you don't have the original dialogue.tlk file in the root folder. It did this to me back in December when the beta came out ( I got the beta because HG was talking about 2 beta servers) and last night when I wanted to look at the new prestige class.
All I did was take my old dialogue.tlk file and put it back in the root folder and all was fine. Why it requires it I have no idea, maybe it's just my computer?