There isn't a way to save or export the Campaign out of Roll20.
I think you might be confusing it with Roll20's automatic backup of our server that happens every night. If there's an instance, heaven forbid, where someone's campaign disappears, we're able to do a rollback to retrieve it.
You can create a copy of your Campaign if you want to try something wild without fear of losing your previous work. If you go to the details page of any of your Campaigns, there's an option to "Copy/Extend Campaign". Make sure you click all the check boxes to ensure that everything gets copied over and you'll have a duplicate of the Campaign on your account to play around with or to have for safe keeping.
