That's strange. Do you mean they deleted their own tweet so your tweet doesn't show up? Or that only your tweet is now gone?
Only my Tweet. I know it was there because when I turned on my phone this morning it was still displayed, but when I clicked on it I got a message that it had been deleted.
Could be that they didn't want their bosses to figure out that they screwed up and missed the pregame event that they were supposed to have attended.