Cara wrote
I have my forum in two places, one in a blog post and one in a post page (I use blogger). Both are identical, showing the same information. I posted it on the blog post first. If I delete the post page one, will the other stay intact, saving my information?
Maybe you should post the links here so that I can take a look first.
Cara wrote
While I'm here, another question: if I accidentally delete the post I have my forum in, does that mean I lose it forever? (I don't have a Nabble login, if that makes a difference)
If you delete the post through the Nabble menu "Delete this post", then it will be really deleted. If you remove the embedding code only, then the post will continue to exist on the Nabble website. I suggest you to register because Nabble sends notifications about deletion and other events that you should be aware of.
Cara wrote
If I save the HTML as a backup somewhere else, would that be enough information for the computer to rediscover the forum - and all I and others have posted on it?
No. If you want a backup of your Nabble apps and posts, you should use the "Options > Download archives" feature.