The devolving of the internet to national intranets is likely, but I don't think it can be done to a big enough extent that it stops Bitcoin. It only takes information to leak through the firewall at one point of entry to make the firewall completely useless. Bitcoin transactions and blocks can be transmitted globally via sat, long and short distance radio, telephone, or the internet, bypassing the firewall through steganography and such. It seems like a futile task for states to attempt to filter it. The Bitcoin protocol will likely be available over encrypted and authenticated transport channels too, meaning that the nation state isn't going to be able to stop it without completely banning encrypted communication for which it has no back door.

That may be attempted, but then no technology company is going to start a business in the locations where this happens. The nations which attempt this will probably do more damage to their economies by enacting it than any damage that Bitcoin could possibly do. It will only take a couple of nations to declare themselves open for bitcoin business, to have economic success, for the rest of the world to realize that fighting against Bitcoin is a losing game.

Debasement of the USD will probably happen, but who knows when. My guess is it that it won't be a sudden event but will happen gradually over a few decades. You might measure USD to lose half of its value over a decade, but if you attempt to do the same for bitcoin, you might find that it has barely changed because "inflation" in bitcoin is negligible - ~7/8 of the total bitcoin supply has already been released, and the amount of "inflation" is decreasing over time.

In my opinion: the latter.