Imagine there being like 3 ppl left in each country that are healthy not dead from the virus

3 survivors in each nation? I think that could well be Extinction for humanity. The breeding population would be so low as to be incredibly difficult to recover. In large nations they'd also have to be able to reach each other. Smaller nation clusters may be lucky enough to come together. In an ideal scenario, the small groups would be near borders with each other. You'd want a very high female to male ratio in the groups. You'd need to learn to hunt, farm, fish, etc. Libraries would become holy places for the knowledge on offer. But soon there would be no power plants operating.