In retrospect, I shouldn't have been nervous at all.
The reunion went well. Very well. My only regret was that my fiancee couldn't enjoy herself as much as I could, since she knew no one there but me. I like to think that she enjoyed my pleasure however, because that's the kind of amazing woman that she is.
Here's what I've learned about getting older, and I learned it at the reunion: (1) Everyone grows older, but they see themselves as always being the same age; (2) Twenty years later, people either look completely different or they look like they graduated yesterday; and (3) A room full of past-friends-turned-complete-strangers do pretty well for a couple of hours.
The only hope I have is that, no matter what the distance, I can fan the dying embers of a couple of these friendships into something better (e-mail should help with that, I think). There were people I remember and looked forward to seeing, but they didn't show (it turns out the reunion wasn't as well-publicized as I thought); I really enjoyed seeing many of my old friends, and I look forward to seeing them again.