Just in from a French Film maker Xavier Gens

Apparently the earlier version of Rogue One featured Saw vs Vader. It explained how he lost his legs on Geonosis and was crushed by something and trapped whilst his lungs were also consumed by this insectocide the empire used to wipe out the Geonosis Insect type creatures.

Vader chopped his legs off.

This story comes from a friend of the film maker because of French Dubbing work and someone he knew has seen the footage.

I can actually believe this back story to be true. The scene with his Medical droid and on Life Support are clearly missing so this Flashback is missing scene. (10 Years before Rogue One)

So now all we are need to know how Chirrut became Blind but can see the Crystals.