I wonder what the USA would do in this situ
The most common FAA response to a complaint of this nature against a pilots actions would be to initiate an investigation to determine whether a violation of regulations in fact occurred. ATC voice and radar records would be reviewed, interviews conducted and an initial finding made as to whether to proceed with formal investigation or drop the matter. Emergency revocation of a US pilot certificate is possible with certain kinds of violations and circumstances.
Pilots flying other than US registered aircraft can typically expect the initial findings and supporting evidence of violation or deviation to be forwarded to the aviation authority for the state having jurisdiction over the pilot and/or the aircraft. Under agreements with other ICAO signatories, this is similar to what US pilots can expect in case of a flight deviation or suspected flight rule violation while operating within international airspace or within the airspace of a great many countries around the world.
These things happen sometimes and international agreements exist to deal with it. It's sometimes unfortunate that countries don't agree in all matters, but that's the way things go.