No offense meant. I was fishing for info. and throwing ideas out. With 25 years of experience, you certainly know more than a newbie like me.
I was thinking if it was on rootstock, you could plant it deep and see if the scion can root on its own in the soil/ deep pot, while on life support, so to speak. And with many grafts, you can experiment more with different soil and depth for a greater chance of success at rooting the scion on its own. It's a round about way but if nothing else works....
Or another idea, if you haven't tried out yet, is to pre-root before air layering by wrapping the unglued electrical tape side facing the bark, around the scion except for the nodes... I am just thinking on tangents and throwing out the idea that I've read from the archives while searching for how best to root/ propagate difficult figs like Black Madeira.
In any case, good luck on your efforts. Please update on what finally worked. I, like others in this forum, would benefit from your experience. This looks like a really interesting case and a worthy fig to expend efforts to propagate.