I also doubt that it was glued (at least from the factory) or that there is any glue that could be guaranteed to keep it from flying off again. I would recommend silver solder or screws, but I don't consider either a DIY job unless you have experience. A competent gunsmith should be able to put that sight on to stay.
Check with our host, George, who does that kind of work or
www.cylinder-slide.com.
Jim