Would it have been wrong for Jephthah to have spared his daughter?

Last week, I heard Pastor Paine talking about the three different kinds of "wait" in the Bible. It's the word after the word "wait" that tells you which kind it is. I didn't think much of it at the time, but fifteen minutes later I was asked to give the next Sunday afternoon Bible study. As soon as I could, I caught up with Pastor Paine and asked, "Can I steal your idea for the Bible study next week?" "Absolutely!" he replied. So it is with his blessing that I am giving this study.

The Book of Questions by Gregory Stock, published in 1987, contains many thought-provoking questions that are fun to ask and answer. Here is an excerpt from the introduction:

There are no correct or incorrect answers to these questions, only honest or dishonest ones. Can you know what you would do in a strange hypothetical situation? Of course you can't, but why let that inhibit you? This is a chance to gain insights without actually living through the predicaments described. Let your self be swept into these situations so that you care about the choices you make. Resist the temptation to escape from a question by denying its reality or by coming up with some complication that obscures the basic issue. Accept that conditions are as described, the odds are accurate, that promises will be fulfilled, and furthermore, that you know this when you are making your decisions. ... If you feel a question lacks detail or is unclear, make an assumption that will correct the problem.

For each of these questions, I'm going to create a scenario for my own use. Feel free to create your own, if you don't like mine. As much as possible, keep your scenario spiritually neutral. Assume that you've already prayed to God and consulted with the pastor, and received no clear direction. The choice is totally up to you.