Then maybe “Imagine that civilization would definitely be destroyed iff there was a...”?
The rest of the post still reads to me as if pandemic + recession is sufficient, not just necessary, for implying extinction. To be explicit, it sounds like you have ruled out the possibility of observing pandemic + recession + non-extinction, I would have thought you’d want to say that pandemic + recession = extinction, rather than the weaker statement that extinction requires pandemic + recession.
It’s easier to reason with a single cause of destruction: see http://lesswrong.com/lw/hw8/caught_in_the_glare_of_two_anthropic_shadows/
Then maybe “Imagine that civilization would definitely be destroyed iff there was a...”?
The rest of the post still reads to me as if pandemic + recession is sufficient, not just necessary, for implying extinction. To be explicit, it sounds like you have ruled out the possibility of observing pandemic + recession + non-extinction, I would have thought you’d want to say that pandemic + recession = extinction, rather than the weaker statement that extinction requires pandemic + recession.
Go with iff for that example.