The end-end-end game is Venus-like conditions on Earth. I find that pretty unlikely though considering that population would be so reduced significantly much before that and industry would be effectively stopped. As long as any biology survives, they'd likely eventually be able to reverse the changes.
I don't see how. As I said before, the Earth has been hotter than it is now. We're currently in an ice age, and coming out of it: that's why we have ice on the poles. The Earth was never like Venus, and never will be; the thing that humans are doing now is burning a bunch of carbon that was stored in prehistoric times. Back then, it was all in plants in the biosphere, when the Earth was warmer than now.
