Should our 16 year old son be allowed to miss his cousin's wedding to attend his high school homecoming dance?

Our niece's wedding is scheuduled for Saturday, October 24th at 2:00 pm with the reception from 4-9:00 pm. It will be held in a location 2 hours away from our home and we have overnight accomodations. Our son's high school is holding their annual homecoming dance the same night. It is a big event for the entire school, and is the only dance for the year for the freshman and sophomores. (Juniors and Seniors have their own separate proms in the spring.) Our son is a sophomore and is very social. Other cousins, from much farther away (10 hours) will not be attending. (Two are in college, and one in high school.) We have a fairly small family on both sides and any absences will be noticed.