You can run clients locally today - worst case, that is always an option. The data is there and the client is really just about the user experience of interacting with it. Pretty much all the web clients can be run on your own machine, not to mention the majority of the clients don’t have to go through App Store approval as they’re web based. Web clients are interacting with relays client side (your computer is querying the relay, not the applications server) too, so they’re really not even set up to ban relays. You’re not coupled to any one client or relay - your identity is decentralized and your content is redundantly stored. What you’re describing would be fairly difficult to accomplish with nostr.
Discussion
The most effective form of this is China’s citizens ability to access nostr. Damus is blocked in their App Store and many relay URLs have been blocked from the entire country. In a lot of instances, relays have just put up a new domain that routes to the same relay and they’ve been able to allow them to continue to connect - we still have people from China participating on nostr. That is a good example of the game of whack a mole that I was describing. And US censorship does not look like that today. In either case, we will continue to iterate and improve.