I've been obsessing about this for a month now. Really obsessing, to the point that my thoughts drift to that in the middle of other conversation. I wonder if I'll be able to stop obsessing about it after tonight. :-/
The good news is that my players are clearly pretty engaged with the game. There have been at least a hundred messages about battle plans on the game mailing list. These have included some nice bits of roleplaying and character development, as well. I've enjoyed reading about Kyle's moodiness, Turok's brooding about the thought of becoming a vampire, and Larissa's emotional preparations. Even some of the ghosts NPCs have gotten more of a personality, including Charlos' reckless dedication and Delyan's extreme bitterness.
And some of the players are very worried about the outcome, which is another sign of being engaged.
What I want most is for the battle to be exciting. I do care about whether the PCs win or lose, certainly, but I care more about having the players on the edge of their seats. What I fear most, on the flip side, is an easy victory. If the PCs can win this battle easily, then it probably means that I basically won't be able to threaten them in this campaign. (In which case, it's probably for the best for them to make such a major step towards ending the campaign.)
If the players don't win a complete victory, on the other hand, it's likely to change the course of the game very substantially. This will probably mean lots of new topics for me to obsess over. :-)