According to Uncle Wyrms notes, if the game died due to lack of interest or RL issues for either players or DM before reaching the keep, then the following would happen:
Somwhere along the journey to the keep, a messenger would overtake the party riding a magical steed. He would inform the party that the Lords of Waterdeep had just received word that the keep had been razed to the ground during a fierce battle between raval tribes of orcs. While ther is not prccise information concerning the number of orcs holding the keep, the attacking force numbered in approximately 900.
The rider carries a letter of condolence for each member of the group, and monetarycompensation for their loss in the amount of 950 gp. (each).
If the same thing occured AFTER the group reached and/or laid seige to the keep, then the outcome would be determined by comparison of the percentage of loss. The side with the lowest percentage (fewest deaths) would have won and gained possession of the keep.
On a side note:
If any of the players wish to play the characters in another game I would be willing to DM it ... sometime in the future ...