SDK -> WebExtensions: Users lose storage if no embedded version used before 57?

Add-ons Development
#1

I’ve read here that developers need to transition from SDK to WebExtensions via Embedded WebExtensions for not losing stored data.
Does this mean that my users will lose all the storage (simple-storage) if I migrate to WebExtensions after the release of FF 57 without having taken advantage of Embedded WebExtensions? Or is there a way to retrieve the data even from within a future WebExtensions version of the addon?

If yes: Would it make sense to publish an Embedded version that does nothing but transition the storage and inform the user that the addon is currently not usable until a fully migrated WebExtensions version has been released? -> And will this be reviewed and released in time if I upload it for AMO on Monday?

#2

Yes
No
Yes
Don’t know

#3

So I guess the 3. answer should rather be “No” -> doesn’t seem to make any sense at all to upload an Embedded version, when it doesn’t get reviewed and released in time.

will the store.json (currently living in jetpack/<addon-id>/simple-storage) still exist somewhere in the FF profile, having upgraded to 57? In this case I could offer the users an import of this file for storing the data to the new browser.storage.