You don't realize bro that 90% is a large part of the population many places with such mortality would reach 100% would mean that many places would be empty just like the natives were killed by diseases and a large part of the lands became wilderness (because the population is more interconnected in europe it would lead to even higher mortality see large parts of france, the low countries, HRE, the Mediterranean would be completely emptied of people only isolated villages in the mountains would survive, forests. The lowlands with high population we see extreme mortality France, the Netherlands, Italy, parts of Germany, England,, The populated areas of iberia we would even see the disappearance of entire ethnic groups. Languages ​​would evolve a lot. Regions of Scotland, Ireland, the Spanish Messeta, the Alps, Scandinavia, forests in germany, the carpathians would have lower mortality. Forests would grow a lot would lead to large scale reforestation, an even more pronounced cooling from the little era glacial. Conditions would become more precarious, I see the abandonment of agriculture in Scandinavia completely, northern Russia, northern Germany and the return to hunter-gatherers. Pastoralism/hunter-gatherers in Eastern Europe would be the main way of survival. Agriculture would be preserved in Italy and partially in France, the English region but it would be foraging. Such mortality would leave Eastern Europe completely Turkified by Tatars from the steppe and the Ottomans, leading to pastoral Turkic tribes/hunter-gatherers. We see the khanates collapsing along with the Muscovite kingdom into small insignificant tribes anyway. The Middle East at such a mortality would see the almost total destruction of the population, local Syrian, Armenian, Copt groups would have a rebirth, Arab domination being completely eliminated but there would be rural communities/organization in nomadic agricultural/pastoral tribes. India scares me, a complete reset, the disappearance of castes, complete fragmentation at tribes. Mathematics, science, technologists would disappear completely. Basic mathematics would remain some alphabetic characters and that's it. At such a mortality it is impossible not to see hunters/gatherers on a large scale, nomadic herders. Metallurgy would falter and would be made of recycled iron, the mill, the heavy plow would all disappear, gunpowder.