I think the trend of demonopolizing currencies is unstoppable, just take time. I argue that this can be part of a new cold war dimension between countries and when some countries block financial initiatives others fund an opportunity. I wrote a little bit more about this vision in [1].
Perhaps a cryptocurrency is unstoppable, but Libra is the same as Visa. Banning Libra is like banning a company like Visa, it's not anything like banning Bitcoin which would be very hard indeed.
> Libra will not rely on cryptocurrency mining. Only members of the Libra Association will be able to process transactions via the permissioned blockchain.
(From Wikipedia)
It's just a payment processor. I don't know why it's called cryptocurrency. If the bar for that is "it uses cryptography" then Paypal is a cryptocurrency because they use HTTPS.
Nothing is unstoppable, nation states have militaries and intelligence services. Both can be very persuasive. Facebook is paying close to no taxes in the EU, so noone here has anything to lose from them simply disappearing.
Even following your reasoning, I repeat the same: states/federations like US, China, Russia, and EU could find a new way to compete and handle power, so we are talking about countries with a military and intelligence balance.
[1] https://blog.coinfabrik.com/libra-association-a-menace-and-a...