Personally, I think it's possible to keep and scale our current lifestyle with changes like growing meat in vats instead of on animals, better power management, green energy, etc. But that's more faith than knowledge speaking.

The big problem is that even those changes are hard. It is much simpler to have giant wars that cull 5-10% of the world population. In fact, we might end up with both: giant wars, and the survivors deciding they don't want more such wars and trying to fix the root cause of them.

Assuming civilization doesn't collapse wholesale, of course…