On Rosh HaShana, which is coming up, we don’t cry, even though it is a day of judgement, because we are happy and confident that BE”H we will all merit a wonderful, sweet new year.
I would think the nidon diDan would be similar. While it’s a serious occasion (and a personal Yom Kippur), and only a navi knows the future, one would hope that some sort of smile would still be in order, BE”H. Look at the many brachos marriage brings: a clean slate, completing himself with his zivug, etc.