There are plenty of threats out there that could terminate all life on our little planet in varying amounts of time. (Solar flares, meteors and supernovas to name a few).
Are there any disasters that could kill all (intelligent) life on Earth but leave astronauts in low orbit alive for long enough to attempt to come back down to earth? (and restart society?)
Can you describe those scenarios into some detail and explain why exactly everyone on earthEarth dies, how the astronauts survive and what the state of the earthEarth is when they return?
For this question you should assume roughly current technology and Earth as the location. Judging formfrom how often food is sent up to the ISS (every 2-4 months and their 45-day food reserve which they have almost needed to start digging into, I'd say 8 months is a reasonable, optimistic guess as to how long the astronauts can wait until they come back to Earth, I'd be happy to be corrected on that number though.
note: theThe amount of survivors doesn't necessarily need to be 3 of course. In fact, I would personally even prefer more than 3 members of the human species to survive.