First off, I think this is a good read. ^^ That said, a few points:
Even if we can't get to the Golden City, we can get to Living Memory through the giant sky vortex that Sphene uses to get there. We have flying mounts, and if for whatever reason those don't work because of wind currents or whatever, the Warrior of Light would be able to make new friends who construct something that can go up a lot (like a simple rocket, Electrope lift, etc) in the same way that we repeatedly demonstrated during Shadowbringers.
But that said, I don't even think that would be necessary. Because when we beat up Zoraal Ja, he drops the device that's necessary for dimensional fusion. And without Scions or Wuk Lamat there to paralyze us with a monologue, we would simply go pick it up, meaning that Sphene doesn't get it.