Most people in the US and other developed countries will be ok. It will be a significant problem and lead to lots of undesirable consequences, but it is survivable. Importantly, these countries can afford to implement measures that adapt to climate change. The countries that are really vulnerable to the impacts of climate change also tend to be poorer countries that will struggle to adapt to it. This will lead to a huge refugee problem in the coming decades, which will be worsened by the fact that impacts of climate change will cause more wars. This process has already started. We will be better off if climate change is reduced and the effects of it are reduced, and we absolutely can use our votes to achieve that.
If you don’t like refugees, you should be concerned about the oil industry.
I don’t think people are going to go extinct…but in the worst case, probably the way the Roman’s went “extinct” and probably for similar reasons except their situation was caused by natural global cooling on a less extreme scale but it did create 1) less food and eventually the economy was in a recession more than not and 2) oppressed refugees who eventually had successful uprisings.