1- Death of the Body- The God falls into the river- the sandtout from his body will spark a new spice-cycle, whose worms will forever have something from Leto- the seeds of the Body
2- Death of the Soul- The end of Siaynoq- but even as the FishSpeakers scatter, new interpretations like the people's Shaitan and Tleilaxu Prophet- the seeds of the Spirit
3- Death of the Myth- the savage breaking of His Peace, which also means that people stop thinking that everything that happens was foreseen by Him- and the Scattering brings about a new stability of sorts- the seeds of the Myth
4- Death of Reason- the end of His world view, of his ideology, his teachings- fading out in time, to be revealed after millennia at Dar-es-Balat- the seeds of Reason
I do think that "reason as purpose" and "reason as capability to reason" are both nuanced in His words. One of the things i noticed after re-reading GEoD was that His words could always be understood in other levels, and those usually did complement and enrich my reading. Even if it is bad English, and i am not even a native speaker, i do find the connotation of "purpose" enriching in this context...
So i would guess that the death of reason is in some ways the death of the GP, as in the moment where people stop thinking "what did the Golden Path require here?" and started thinking "what should I do here?" -- and that in many ways is also a seed of the GP, a return without a resurrection, so to say.
Anyway, i re-read the chapter, and i do really think it all is trying to explain the Royal Death and it's consequences...
"Each of us is different in the way of Moneo's observation," he said. "Genesis does not stop. Your god continues creating you."