system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What would the astronauts on the ISS do in the event of a cataclysmic event on Earth that wiped out the entire population? Is this a scenario that has been discussed by the various agencies?
gpt
That's little more than a thought exercise, because there isn't much point in making a plan on what three people would do in the event that the 7,000,000,000 people below all die. The scenario is so unlikely that it's not really worth training people on.

But, to continue the thought experiment, it would really depend on the nature of the cataclysm. Because pretty much anything that would wipe out all the people would make it unsafe for them to leave the ISS. So, at some point, they have a choice... stay in the orbital coffin, or take the Soyuz back down to the giant graveyard below, where whatever killed the rest of humanity is probably going to kill them too.

TL;DR - They will die.