I've always said that for a film medium, Follies needs to have 2 incredibly powerful leads - Sally and Phyllis. Phyllis should be taken from the film world, as her role is flashier, and more "likable", plus the fact that her vocal demands are far less taxing. Sally, as the emotional center of the piece, needs to be from the stage. I would personally live Bernadette to reprise her role. I loved her take on the role.
As fir the script - I say leave it as it is, open up the scenes to the entire theatre, and briefly outside for "Mornings". It'll never happen, of course, but in a perfect world.
"Sticks and stones, sister. Here, have a Valium." - Patti LuPone, a Memoir