Will computer RPGs like NWN replace pen and paper D&D? - not a hope. Pen & paper D&D allows the player and DM to do virtually anything. For a computer RPG to allow that flexibility, it would have to be several magnitudes more sophisticated that NWN will ever be.
Pen & paper D&D is in danger, but not from CRPGs. It is in danger because it is in the hands of a large company where the bottom line is the end all. Read what Monte Cook has to say on this.
http://www.montecook.com/lineos.html
But that is another topic altogether.
Back on topic - If I were to blow the dust of the ol' crystal ball, this is where I see the future of D&D eventually taking us.
Computers will be seen more and more at the tabletop. A number of DMs currently use laptops as aides. Players are starting to use handhelds. This is just scratching the surface.
Improved handhelds are being developed, as well as tablet PCs.
The stuff I have seen on the tablet PCs is amazing. All the power of a full sized laptop into a computer slightly bigger than a iPaq or a Palm, with a much larger display. With built-in wireless networking.
Imagine the possibilites with the right developed software - the DM can have his battlemat right on tablet PC. He sees and manipulates everything. With layering, the players see the same map but with only what the DM wants them to see. A player moves his character with a drag of his stylus - everyone sees the action update on their PC. The character enters a hex or square the DM has setup as a trap. The software sees a triggered event and resolves it automatically, by seeing who else is affected, resolving the saving throws, allocating damage and automatically updating the player's character sheet, as well as the DM's character management module.
The DM calls for initative rolls - the players use the dice program to make the initative rolls. Automatically, the initiative order appears for the DM, along with the monsters inititative. The DM activated the initiative count down and the player in question get a pop up informing him he can do his actions.
For the monsters, the attack rolls and damage routines are automated for the DM, freeing him to concentrate on tempo and cinematics for the battle. Character sheets are automatically updated as the result of damage or ability loss.
You start to see the potential. Less disruption of the game resulting when the player or DM tries to round up enough D6s for the 20d6 Horrid Wilting, or to resolve the 6 - 8 attacks and damage of a monster who has that number of attacks.
More time playing, less time pausing the game to roll mountains of dice or to resolve disputes on who is where or who did what.
Less time drawing out a room and putting minatures and terrain out while the players wait to see what is going to happen.
IMHO, this is where D&D is heading. It is slowly going to evolve from a purely pen and paper game into something more to do with computers, but less than what we have come to accept as the norm in CRPGs.
So pen and paper D&D will not be surplanted by CRPGs..... but pen and paper D&D will evolve into something more to take advantage of the power of the computer.
My two cents....