Offhand I recall two who made dubious vows and followed through: Hannah, who gave away her son, and Jephthah, who murdered his daughter. To me, in both cases the Lord would have excused them for reneging. They appear to be cautionary tales against rashly-made vows, precisely what the verse you cited warns against.
Yes. Hannah missed the blessing of raising young Samuel until he was a young man with her vow.