The problem isn't population - population is actually leveling off. The problem is energy use. We're going to be living in different places, and we're going to be living differently, but we're going to be living. Realistically speaking, if you're typing on a computer in English and worrying about your grandchildren, you're going to be fine. It's the brown people without running water that are fucked. They'd be a lot less fucked if the developed world learned how to use energy like sub-saharan africa.
We also need to take into account the very bad things that seem to be happening to marine life and insects. If whole ecosystems break down, and food chains no longer function, we could all find ourselves screwed in ways that are not obvious until they're upon us.if you're typing on a computer in English and worrying about your grandchildren, you're going to be fine