I am getting fitted to wear "Ampleye" RGP Scleral lenses from Art Optical. I called DAN and asked about diving with them and DAN said there is no reason I can't dive with any RGP Scleral lens. They are so large there is virtually no chance of them coming out with a flooded mask.
I'll be diving with them in a month (mid-August 2016), so feel free to PM me if you have any questions.
I am excited at the prospect of being able to dive and actually see well!
If and when you lose a lens in your mask, just relax and go with it. I think with keratoconus you can still get your gauges close enough to see them! I wear a mask with a purge valve in part because I have been able to clear it without losing my lost lenses to the ocean. If I lose my left lens I can't see my gauges without getting them really far away or really close and if I lose my right one everything in the distance goes really blurry. But not any worse than no mask at all. Uncorrected I'm about 20/400 in my good eye.