It's a hot mess too. When you have an American carrier / phone number on an international plan and they shut down all radios in the case of an emergency in the EU, you still get 2G/3G service abroad while everyone's phones around you is dead.
What do you mean? They are shutting down the radio transceivers for 2G/3G, how would an American number/carrier get a signal in countries that have shut down their 2G/3G networks? Or are you talking about plans to do direct-to-cell satellite service, cause none of those are 2G/3G as far as I can tell?
The whole point is to free up spectrum, how would that work if that spectrum is still in use for the American carriers in countries that shut down the service for domestic use? Why would service be maintained for such a niche usecase?