That worst case scenario here is not plausible unless you envision something happening many centuries in the future, perhaps. I think it probable by then we'll have mastered other means of producing energy.
Even a 7°C rise would not render the planet uninhabitable. It would be bad for many obviously. But I don't think any sensible person is worried about the planet becoming like Venus.
I still would like to see the outline of a plan instead of just warm and fuzzy vague general notions.
I think that one of the things we bank on as humans is that climate is generally comprised of negative feedback loops. Usually one thing happens that swings us in another direction, and the consequence of that is an effect that puts a brake on the result of the first thing.
If climate in general were comprised of positive feedback loops, it's unlikely that complex life would have ever developed on Earth.
I think some of the hubris of humanity is taking that idea, that generally climate is self-regulating, and discounting the chance of something which pushes it out of its regulation zone to where you can have runaway effects. And I'm not sure you can state that those runaway effects would be "centuries in the future", as we don't know where/when the tipping points might be.
That's why I bring up the 5 mass extinctions in the planet's history. It's happened before. It will happen again. Whether or not it will happen this time, due to this cause, is a complete unknown.
I don't think anthropogenic global warming will trigger the next global mass extinction. But I'm not going to say it can't, or that it would take centuries, if we do actually hit a climate trigger point where positive feedback dominates.