There’s another possible wrinkle here. John says in his Q: “I did not really expect this many people to say they were coming to my 50th high school reunion.”
Native speakers of English automatically and unconsciously distinguish between “coming” and “going” as movement toward and away from the speaker (even if we’ve largely lost it in “bring” vs. “take”). The sentence above strongly suggests that John still lives in the town where he went to high school and that the unexpected attendees are coming, not going, to the reunion. Right, John?
So there’s a possible awkwardness for him in not attending an event right in his own town, as if, instead of just passively not going, he were avoiding it for some reason. That may call for more explanation and produce more discomfort than the anticipated discomfort of attending.