As to the hanging threads...I think it all depends on what your writing how important the threads are to tie in. I will give you two examples.

In one of J.R. Wards Brother Hood Series Novels. She sets us up with several scenes that seem to include a former member of The Basta*** hiding out in the attic of this old mansion turned bed and breakfast. The place is thought to be haunted. We get a lot of flashbacks and we know who he is connected to. The problem is that by the end of the book, shes forgotten him completely. It's like she set him up to causes issues with the woman he is connected to and John her future mate, changed her mind and didn't edit it out. There have been at least a couple of books since then and she has yet to address it. It is driving me crazy. Why leave him in the story if your not going to use him? I mean the brothers don't travel there or anything. It's just several scenes of this ghost hunters show filming there and a few scenes of him watching them and flashbacks to connect him to the woman.

It is driving me nuts. Do not leave a thread hanging like that.

Then there is a song that hit the radio about 22 years ago called Don't Take The Girl by Tim McGraw. He never tells you in the song if the doctors are able to save her. He leaves it up to us to decide. I thought they did. My aunt said no way. I was pregnate at the time and she was dieing of pregnancy complications so Clanbear refused to listen to it. He couldn't handle even thinking about the possibility.

Though he does clarify in the video for the song and Mom survived, In a world without videos it would have been perfectly fine for him to leave it for the half empty/half full crowds to argue over to the end of time. You get to believe what you want to believe.

So in cases where allowing the reader or listener to believe what they want to believe, leaving threads untied is perfectly okay. However, dropping whole threads that don't have a purpose of being there if you don't tie them in and that you don't intend to pick up in a later book leaving your readers scratching their head and annoyed... Not such a good Idea.

Lucky for me I guess enough of us were irritated over it that it seems she is going to close a bunch of loose ends and dropped threads with the next book and I am praying its going to be that one with the ghost hunters. She has an awesome editor. I don't know how she let her leave that in there.