the Theme isn’t responsible for the content you add to the page.
I am not a user of WP Bakery so i am not sure what happens to the content if that plugin is disabled but at the very least it would remove any styles you added in WP Bakery.
Unfortunately migrating from a page builder to a non-pagebuilder site requires manual re-working.
@David Thanks. Would be possible to use a scraping/cloning tool to copy all existing pages into a clean installation of Generatepress and then move the data back to the original hosting? Is there a scraping/cloning tool that Generatepress supports well?
I would probably create a Staging site. Most good hosts offer the service.
Then on the Staging Site switch themes and disable the page builder and see what breaks and what does not – and then repair / rebuild from there. Once happy your Host can push the Staging site to live.