I also doubt they'd come or be invited, but if they did, they would be protected by the Vienna Convention (https://en.wikipedia.org/wiki/Diplomatic_immunity http://legal.un.org/ilc/texts/instruments/english/convention...). The US could break that, but not without serious consequences for their own leaders and diplomats abroad.

Could the ICC issue an arrest warrant? Yes (https://academic.oup.com/jicj/article-abstract/7/2/315/90220...) if only the US was a participant in the ICC.