I know it's a bit late to mention this, as many holiday parties and such have already taken place. However, my fiance works in the service industry at an upscale chain restaurant, and it is astonishing how many people book a large reservation for an office party and then simply don't show up.
Keep in mind that servers often count on having that one large table's tips as most of their pay for the day. They have to spend time putting several tables together and putting out extra place settings. They are given no other tables while they are waiting for this large group. In hopes that the group is running late, the server will often wait an hour or more after the reservation before they decide the party isn't coming at which point they have to break down all of the tables and, often by this time, the lunch/dinner rush is over and they take home virtually nothing for the day.
So, if you know that your office changes restaurant locations or cancels a party altogether, make sure the person who is handling logistics has called the place to cancel the reservation, as it may slip their mind. Even giving last-minute notice is better than nothing (though advanced notice is ideal and always appreciated).
All it takes is one phone call.
Thanks for reading and happy holidays!