Climate change is not a binary "no harm" vs "worst case" situation where you cross some magical tipping point from one to the other. It is a continuum where the more damage you do, the worse things will be. Even if we are already doomed to some major troubles in the future, there is never a point where it makes sense to give up because it can't get any worse - it can always get worse.

Right, but it’s not completely linear either. There are tipping points, such as a collapse of the arctic ice sheets, savannaization of the Amazon, arctic methane release, which could kick off their own positive feedback loops that cannot be stopped by humans.

Certainly we can do things after that point, but we’ll see much more diminishing returns.

James Lovelock's last books certainly would agree with this.

Perhaps we may get lucky and some event could throw things the other direction, like a large meteor impact or wide scale nuclear weapons discharge (leading to a lengthy nuclear winter.)

That's very well possible.