You can automatically sync all of your work on Slides to Dropbox. Enabling this gives you automated backups as well as full offline access to your decks. To enable this feature, open the Export panel in the editor sidebar and follow the instructions there.
Once enabled your decks will automatically be copied to Dropbox each time you save. To view your offline decks navigate to the /Apps/Slides App directory within your Dropbox folder and open any of the deck HTML files. The deck will open inside of your web browser but since it's only using local files it works even when offline.
Note that files are only copied from Slides to Dropbox. Meaning any changes you make to the files in your Dropbox will not be copied back into your hosted Slides.
It's possible to access a speaker view for your exported presentations. This speaker view includes any speaker notes that you may have added through the Slides editor. To open the speaker view press the "S" key on your keyboard while a presentation is open in your web browser.
To disconnect and stop changes on Slides from being saved to Dropbox you'll need to head to the Dropbox settings page and remove Slides from the list of apps. The settings page can be accessed at https://www.dropbox.com/account/security#apps