I've been using Adventuron for over two years now and I've never lost changes that I have saved with ONE exception:
If you save in incognito mode then the changes will not be saved. Make sure that Adventuron is always loaded in non-incognito mode. It requires access to the web data store, but in incognito, this is removed when the incognito tab is closed.
Saving a backup is always recommended, hence the save-file option.