Hi,
You should be able to do that.
The “Remove Imported Site” option only removes what it added.
Pages and Posts added outside of site library’s import content will be retained.
That said, if you’ve only edited the pages and posts imported by the site library to add your content in, then your worry is valid as they’re removed regardless of what is added/edited within its contents.
Although, before removing imported site, you may want to consider exporting your pages and posts to a file through WordPress’ default export tool via Tools > Export.
After exporting the posts and pages, you can do a “remove imported site” and import Abstract and then re-import the pages you’ve exported.