If 99% of humanity simply disappeared, the remaining eighty million humans would mostly be able to get by on the available resources.

The biggest problems would be fires from untended gas mains, pollution from abandoned chemical storage facilities and industrial plants, and also abandoned nuclear power plants. Feral dogs would be an issue, a lot of domestic cattle and sheep would die off in the first year in northern climates, and the rapid decay of processed fuel supplies—gasoline is not chemically stable in storage—would be a serious problem.

As an example, consider that Belgium, a small, developed nation, would have a population of a hundred and twenty thousand in this scenario, all living within a two to four hour drive of each other. Organizing that population to salvage and make use of available food and energy resources could be managed in a few days.

The same would be true in almost every nation in the world. Ohio would have a residual population similar to Belgium. South Korea would have population of a half a million. Brazil would have two million inhabitants, mostly scattered along its Atlantic coast.

As we know from common experience in dealing with natural disasters around the world, the survivors of a disaster not involving a actively hostile environment (nuclear winter, zombies, aliens, etc.) would mostly try to maintain some semblances of their old communities and relations.

The kind of sociopathic gangs you see in post-apocalyptic survivalist movies and stories would either not occur or would be quickly snuffed out by people organizing around new family and village communities. They would have the advantage of numbers and would know just as much about weapons as the survivalists and thugs.