What would happen is that some of those countries will switch to a different geopolitical block. It's difficult to make a proposition to a country with a foreign army stationed in their territory, maybe because they lost a war 80 years ago or needed help not to lose it. It's easier if that army goes back home. If the USA want to give up their empire to China or Russia, they start with closing the bases. The fallout is economical as well, because American culture and products are going to have more competition and less reach.