This is nonsense. (And your own source doesn't support the claim that the consequences of global warming will be unmitigable for anyone.)
Many parts of the world will become milder for human occupation as a result of climate change. And nothing realistically forecast is unavoidable with wealth–rich countries will A/C and seawall their ways around the consequences.
Edit: the report’s "Extreme" severity band is indeed not a forecast but they’re basically saying "the chance of this happening is way too high".
Many effects would hurt most people. But some would also be profited from. It’s incredible–as in debilitating to one’s credibility-to claim that everyone would suffer in the extreme case.
The rich, and I say this broadly to include the rich countries, will probably be fine. Poorer, yes, but not uniformly. Plenty of plenty of places and people would see booms from the new weather patterns, coasts and social fault lines.
Please also consider infectious disease and famine throughout the world.
You can hide from the temperature. You will have a harder time hiding from war and disease.