Sober analysis, as always, however I don't think we have these long decades that you speak of. This is where the "2" punch in the 1-2 combo of resource depletion and the climate crisis comes into play. Quite simply, it won't just be more expensive to grow our food, but increasingly large areas which are now "breadbaskets" will be disrupted and eventually rendered all but useless for agriculture due to extreme weather. The remaining ones, as well as the ever more precious water sources will become equally, if not more, valuable with fossil fuel deposits. All of them will be contested and resource wars will most likely ensue.

While it's impossible to make any predictions, I think it's likely that such conflicts will in fact accelerate rather than decelerate the collapse, and the endless streams of refugees such as we haven't known before will put even more pressure on governments to close their borders, and fortify themselves behind isolationism and nationalism.

The best-case scenario (barring some kind of energy miracle, as you put it) would be humanity ending sometime around 2100. Worst case would be sparking a nuclear conflict and ending ourselves much sooner than that.