How much does the rest of the world need USA?
ESA can ferry 7 tonnes a time on ATVs, and maybe eventually recover items if the ATV is fitted with a return transfer vehicle. Longer term, the ATV may become man-rated, although whether that would fly on a man-rated Arianne 5, or Arianne 6 I don't know. The Arianne 6 is only a theory at the moment, but at this rate it might be here before the new Nasa beast!
Russia is able to send up progress supply ships, and Suoyez people carriers. They can also return people and a small amount of stuff.
Japan can also send up stuff with their HTV (As long as there is a keen video game player up there to catch the HTV in mid flight and dock it using the arm).
China wants to get in on space stations, and it wouldn't be a bad idea to join the party for a heads-up before trying to do it all by themselves for the first time.
There are a fair few items up there as spares for things too big/heavy to send up on Progress / ATV / HTV.
What I don't know about is ground support for the main station by anyone other than NASA.
So if USA / NASA go home and abandon the party, can the rest of the world carry on without them?


