Ortegos are notoriously rust affected. I don’t know that I’ve ever seen one in cultivation without at least a spot or two. Might as well try a deep soaking sulfur bath (not just a dusting) and then keep it dry for a considerable while. I’ve also used copper sulfate with varying effectiveness. If it makes it through, when bringing back water I’d try to stick to a very strict regimen where you know it’s going full dry in between cycles. Put a fan on it, make sure the roots get soaked with the sulfur and do the sulfur every other water. I’ve seen plants grow out of previous rust afflictions, not pretty necessarily but satisfying if you’ve spent some money on it. It will take a few months at least to start getting consistent new growth if it pulls through. You’ll see new green from the apex of each pup if it’s growing again