That is a totally valid concern. There is no guarantee that Keep (or any online service) will be decommissioned. As of now, there isn't a desktop application for Keep that saves notes for offline access (though you can still access notes in airplane mode on your phone)
Yes, they do, but it just shows you what the features are and doesn't teach you how to use it effectively - and how to make the most use out of the features. This guide covers both the what and the how.