At present, there is no way (we know of) to export data from Ning other than RSS feeds (found at the bottom of most pages). The best way to be in control of your data in the form of a full-scale blog (including meta-data) would be to host it elsewhere. You could still cross-post content by copying it to Ning as a forum discussion or blog post, but your content would be safe and under your control via the external site.
While some services, like MediaWiki, Wordpress, and Google Wave have optional LaTeX plugins, apps or support, Ning does not offer that functionality. It is one of the trade-offs for being really easy to create, design, and edit by most users regardless of their computing ability: nothing about Ning is too complicated or specialized. As a result, it lacks some flexibility. Also, site owners relinquish a lot of control to Ning and have only limited access to source files for the site infrastructure.
There may be some workarounds for mimicking LaTeX-like typeset by rendering LaTeX online with output in the form of images (for embedding) or PDF documents. I have found this site, which seems to offer a comprehensive array of alternatives of this kind. Having said that, I should mention that I am really not experienced with making any of this work, as I don't use LaTeX personally. Perhaps someone with more direct experience will be able to provide more detailed advice.
It is worth mentioning again here that admins and network creators can't archive any of the forum, blog, photo, video, group, or any other data on this site on behalf of its members. Ning may offer this in the future, but, as yet, we can't download or backup this material. So, unfortunately, it is up to members to self-archive their own contributions if they want them to be saved. Also, if the member who started a discussion or post leaves the site, deletes the post, or is banned, all of the responses to that thread also disappear. If you're going to be doing a lot of elaborate blogging, it may be best to cross-post content here, rather than host it solely on Ning.