The reason the Galaxy class's saucer separated from the body was to avoid putting civilians in harms way. When going into combat, separation would allow them to leave all the civilians safe and sound. The only problem was that the special effects were a bit expensive, and the feature become less prominent as time went on. There were many times when it could have been used but it wasn't.
The Prometheus' seperations system, being substantially faster, actually increases the viability of this strategum, as well as it's use of seperate warp drives for all of it's sections.
If the Galaxy was designed with a fast automated seperation system similar to the Prometheus, and a seperate warp drive for the saucer, there would have been little problem leaving the civilians behind in most cases. It would have been a simple matter to keep both bridges staffed, so that the saucer could seperate and leave whenever things got hairy.
The Prometheus' seperations system, being substantially faster, actually increases the viability of this strategum, as well as it's use of seperate warp drives for all of it's sections.
If the Galaxy was designed with a fast automated seperation system similar to the Prometheus, and a seperate warp drive for the saucer, there would have been little problem leaving the civilians behind in most cases. It would have been a simple matter to keep both bridges staffed, so that the saucer could seperate and leave whenever things got hairy.