Even if your definition of "oil left" is when EROEI hits 1:1, that still doesn't mean we're out of oil, since there's applications for oil that don't involve extracting energy for it. So it'll continue to be mined even when we're losing energy by doing so.
Now, I probably should have picked a better comparison, since oil really is zero-sum in ways that needing to grow more food isn't.
The point is that in an alternate universe where agriculture was 40% less efficient it doesn't follow that there would be 40% fewer people. Rather, more of the gross world product would be spent on agriculture, since there's a lot you can do to throw more money at the problem to increase yields, and pricing would do a lot to increase the efficiency.
Well, sure. Earth's population has grown roughly 100% in the past 50 years, largely due to the advances of Green Revolution agriculture. This isn't just nitrogen fixing. It's advances in mechanization, transportation, finance, preservation techniques, and more. All of those things would have happened (more or less) even without fixed fertilizer.
I disagree with the idea that there'd be proportionally less meat, for a couple of reasons. First, a lot of grazing-animal meat (beef, basically) comes from land that is unviable for plowing or other vegetation farming. Second, in the absence of inexpensive chemical fertilizer, manure would be a much more important fixer, just like it has been for thousands of years.
Now, I probably should have picked a better comparison, since oil really is zero-sum in ways that needing to grow more food isn't.
The point is that in an alternate universe where agriculture was 40% less efficient it doesn't follow that there would be 40% fewer people. Rather, more of the gross world product would be spent on agriculture, since there's a lot you can do to throw more money at the problem to increase yields, and pricing would do a lot to increase the efficiency.