I realize this is an old thread, but it's the only one I found on backing up flows. (Simple searches for simple minds)
Currently, Share a Flow to Drive only saves a link to the current flow on the Stringify website. No restore possible. I then tried sharing that with Evernote. All I got was the description. See next paragraph.
The Description of the Flow is for the first iteration. I've made some massive changes in a flow, including removing the original button trigger. The description still has the button trigger, and the very simple elements of that first saved flow.
...or some other method of recovery when one has shot one's self in the foot programmatically.
Ability to generate new description when Flow is redesigned.