Levels of global catastrophes: from mild to extinction
It is important to make a bridge between existential risks and other possible risks. If we say that existential risks are infinitely more important than other risks, we put them out of scope of policymakers (as they can’t work with infinities). We could reach them if we show x-risks as extreme cases of smaller risks. It could be done for most risks (with AI and accelerator's catastrophes are notable exceptions).
Smaller catastrophes play complex role in estimating probability of x-risks. A chain of smaller catastrophes may result in extinction, but one small catastrophe could postpone bigger risks (but it is not good solution). The following table presents different levels of global catastrophes depending of their size. Numbers are mostly arbitrary and are more like placeholders for future updates.
http://immortality-roadmap.com/degradlev.pdf
If only one village survive, it will use scavenging of nearby city for decades and during this time it will lost most high educated people.
But lets assume that scavenging economy is no possible, may be this village survive on remote island, which is probable, in case of pandemic.
In this case the main problem will be economy of scale, chemistry and raw materials. Even 19 century economy is based on available coal, iron ore, copper and some other things. Most of them require very specific people, knowledges and instruments to find and produce.
And also they are economically useful only if it is done in the medium size european country.
And finally most ores which were easily available in 19 century are now depleted or not present at all in remote islands. So if a village survive on an island it will not be able to build steampowered ship in next few years to explore surrounding. I also would not overestimate the ability of random people to study new science like geology, using only books, without proper training and control.