Ultimately, this is something I wouldn't worry about. As with any other Mozart based speakers, once you have set up the Theatre to your liking, there shouldn't be any need for further app or software updates (although B&O do continue to provide ongoing updates both both the app and the product software if you choose to install them).
You can use the Theatre with a B&O remote without needing the app, but if you have an iOS or Android device with the B&O app installed then this would in theory continue to function long after B&O stopped providing further updates.
I have my own Mozart speakers set to not download further software updates, as I am happy with their current functionality (I may review this if B&O provide extra features in the future!). So, to all intents and purposes, my speakers are operating in that same (theoretical) "end-of-support" situation that you described.
Hope that helps!
Kind regards, Steve.
Location: The cable workshop, England
My B&O Icons: