I’m on the last month of an Audible trial. If I use my credit to preorder a book and then cancel my account, will I still get the audiobook when it’s released in November?
You should, just as you retain the ability to access any of the books you've already bought.
Yes. When you use a credit for a pre-order, that credit is deducted from your account immediately. You now own the book, so you can safely cancel your membership. You're just waiting for delivery of a book you've already paid for.
I did that a few months ago and add no problems, I canceled in april and the preorders where for august and the books where delivered in the lauch date