That's the endgame I expect: climate refugees leading to (possibly nuclear) war. With a much smaller human population (and perhaps a bit of nuclear winter), atmospheric CO2 will return to pre-industrial levels, and things will return to normal in a couple millennia. The remaining humans will migrate down from Alaska and Siberia, and build new cities on top of the ruins.
Climate change is a "solved" problem, but the solution isn't something I would want to live through.
I can see advanced civilization taking a (possibly long) pause. But there will be so much space to expand into for the survivors, and caches of technology to discover. Someone will eventually discover and re-tool.
