Thanks to the mystery reviewer who sent the quick feedback on my theme submission
A point of feedback was "Activating theme will override all your existing pages. It does not have a fall back for the menu that will allow to get your original menu settings back. "
I’m not sure what that means. I’ve switched themes on my local install a number of times and the menu stays constant, is this fallback still required?
I don’t think the fallback is required. I don’t have one on my custom themes. I’ve just tried switching between themes on a test site, and I didn’t lose a menu. (The menu locations might not match up, of course, but the menus themselves remain intact.)