Oh absolutely without actual government action the overall population decline will be catastrophic. Basically if it's handled the way that climate change has been, our kids/grandkids/great-grandkids will be screwed because it's a similarly significant world-wide challenge for humanity that like climate change will require some changes to how people live and run the world. However, unlike climate change, population decline won't necessarily kill off humanity entirely, because it will self-resolve one way or another, either by society collapsing due to the medical system collapsing or by actual social change to adapt to the normalizing population level