If OD dies, will 1/2 continue working? A/OD trans?

As far as your question is concerned. If od does go out, yes the rest of the gears should work. Just depending on what is going on in the transmission? I work on "gm" vehicles. And I had a 84 olds with over drive that went out of it and the other gears worked, but the longer I drove it the other driving gears begin to fail as well too much pressure on the other gears. Finally about 9 months later the reverse finally went out of it and I had to rebuild the trans.