Also an economy that requires an infinitely growing population feels like a pyramid scheme which is also an unsustainable system.
Or not. It could be oscillatory and humanity could cyclically reverse-decimate itself while the descendants of the survivors get to enjoy millennia of the fun part of the pyramid scheme.
The big losers are whoever is part of the "perish in a holocaust" generations, and probably the first couple bootstrapper generations afterwards.
Only if we don't explore and colonize the stars. From what we know, the universe is infinite.
And, before you suggest it, no, there will never be faster-than-light travel, and even relativistic travel is super unlikely.