The last time I saw Fleetwood Mac, I believe that they demonstrated a neat trick to address this issue. Every time Stevie Nicks had to go to her highest registers, two "sound alike" back up singers joined in. They were subtle enough in the mix enough to preserve her timbre and the illusion that it was Nicks, but audible enough to convey the note.
I was impressed: The songs worked despite the natural decline in her voice and showed that a creative work-around can help diminish (tho not completely eliminate) this essentially inevitable problem.
I was impressed: The songs worked despite the natural decline in her voice and showed that a creative work-around can help diminish (tho not completely eliminate) this essentially inevitable problem.