What sort of technology can be used for people with untreatable retinal detatchment?

Not much. A low vision specialist may be able to help if both eyes have poor vision. If only one eye has poor vision, then polycarbonate (shatter-resistant) glasses are recommended to protect the better-seeing eye from any unintentional trauma.
Low vision therapy. When vision can't be restored surgically, a referral to a low vision specialist is helpful to teach people to use their remaining vision using magnifiers and visual aides.