I clarify:
Let’s say scientists can’t come up with solutions to global problems, AI gets out of control and turns almost everyone into paperclips during wars, and in the 2040s or 2050s, the surviving people (about a few tens of millions around the world or even less) gradually return to the level of intelligence of their distant ancestors?
The world can support less than 1% of its current population if everyone reverted to a neolithic lifestyle. And countless species would be hunted to extinction during the collapse.
So in short, the answer to what I would do? Like nearly everyone else, just die. The folks from Sentinel Island will inherit the Earth.