Atari representative, MattLab announced in this forum thread that a digital download of Mask of the Betrayer is available at Atari.com:

Atari, Inc. is pleased to announce that the Digital Download version of Neverwinter Nights™ 2: Mask of the Betrayer for the Windows platform is now available on http://www.Atari.com/us.

Neverwinter Nights™ 2: Mask of the Betrayer will present players with an exciting new campaign, epic levels, dozens of new feats and spells, new races, base classes and prestige classes, new companions, new weapons, armor and crafting options, hordes of new monsters, and enhanced modding tools. This is an expansion pack for Neverwinter Nights™ 2 and requires the original NWN2 game to play.

For More Information on Neverwinter Nights™ 2: Mask of the Betrayer please click HERE

Features:
1. Challenging 20-30+ hour adventure complete with strategic action, a rich story and deep characters.
2. Advance to Epic levels (above level 20) and choose from over 100 new spells and feats.
3. New toolset features and improvements make creating your own adventures easier than ever.
4. Includes new monsters, weapons, items, classes, races and environments.

To purchase a copy of Neverwinter Nights™ 2: Mask of the Betrayer for your PC in Digital Download format. We are offering it on our website right now!

Why wait? Start playing today!