

There might indeed be ways around the filter, e.g. a stable, non-exploitative society but they would never reach space. The filter might indeed not even exist, space could indeed still be young but I’m not very convinced. If space were young, and if it were to expand as it currently does, civilizations would have fewer opportunities as there would be fewer visible stars to explore. As time grows, chances get smaller still.
Let’s say humans do cling on. I believe they will face challenges that are too steep to make long-term survival probable. Not only the heavily pollution and the unlivable climate, but the depletion of basic minerals will probably prove too great an obstacle. That band of humans must have held on and maintained all current technology, and have sufficient power sources, to be able to do some deep underground mining, as all easy-to-reach minerals have already gone. Without technology or those minerals, I’m not sure how we’ll be growing food or cleaning the air to breathe.
Well put! :)