Game Banshee has an interview
with Kevin Saunders, the lead designer on this project. Tragically, I don't think we'll be seeing our companions (at least from the get go) in the expansion:
"Mask of the Betrayer begins almost immediately after the ending of NWN2. You will play your same character (if you wish), continuing his or her story. (Your weapons and gold are gone, but youíll have many of your other equipped items still.) While the story in Mask of the Betrayer is connected to Neverwinter Nights 2, you donít have to have played the expansion Ė the story stands alone, but players who have gone through the NWN2 campaign will recognize some references that occur in NX1."