If tear had progressed to retinal detachment would it become a constant loss?

Yes. Signs of rd are those seen by examining eye doctor: subretinal fluid, retinal tear, pigment cells in vitreous, and pvd. The symptoms that a patient experiences are painless, progressive loss or greying; of vision which may involve the central vision. This may be proceeded by flashes and floaters. Sometimes an rd can by asymptomatic, and therefore it is important to get checked.
It can. Retinal detachment causes loss of vision in the area corresponding to the detachment, which will not improve without surgery or some other re-attachment procedure. With treatment, often the vision can be salvaged, although it may not be as good as before the detachment.