Thanks again, everyone!
Last night, I emailed the chief organizer and cc'ed my supervisor. JenJay, I loved your response so much that I used it almost verbatim!
I heard back from the chief organizer again this morning. Her response: "That's too bad. Well, just bring some snacks and we'll help you hide them!"
I've already used JenJay's wording, so at this point I've technically committed to leaving before the dinner portion of the party. Some other posters have some great suggestions regarding getting dinner elsewhere or trying to move the venue entirely, but at this point, I really just want to stick to drinks. I think I mentioned in a previous post that it's a huge pet peeve of mine when events mushroom like this. In my head, I committed to just a cocktail hour over a week ago, so I'd really prefer not to scramble to come up with a workable dinner option at this point (the day of the party). Does that make sense?
Oh, and a quick clarification for those who are wondering whether all the planning is being done via email: In a word, yes. My office just moved to a new building recently, and only part of our office space is ready for us right now, so the entire company is literally crammed into one room. We don't have enough desks for everyone to come into the office every day, so we have rotating "in-office" schedules and 50% of us work from home each day. There are people I work with closely who I haven't actually seen in weeks because we're never scheduled to be in on the same day.
Though that does lead me to one last question: I'm in the office today, and I've had several people come up and offer me food I can't eat. I try to keep pretty quiet about my diagnosis because I think it's unprofessional to blab about medical stuff to colleagues, but it's just occurred to me that between me keeping quiet and the rotating schedules, there's a good chance some party attendees (not the organizers) are going to have no idea I can't join in for dinner. Would it be a good idea to send a general email to the people who I know are going and briefly explain? (I don't even know the full guest list...)
Just saw lowspark replied while I was posting: I admit I haven't checked the menu at the other place, but I sincerely doubt it. They're both very similar "bar food" type places, and the first place was so incredibly clueless (and didn't care that they were clueless) that I imagine the second place would be much the same.