I guess, the important question is what happened to the app copies already installed on the phones? Do they still work? Can they still receive push notifications?

If they're still working - it's much less of an issue. The fact of pulling the app is still serious but surely everyone who wanted to participate had the app pre-installed for a while. If that's the case then Russian tsar's demands for pulling the app off the AppStore are just another example of your classical bureaucracy fuck-up.