I love this song. It was never meant to be a duet. Minnie died before she could finish the song, and her husband/producer Richard Rudolph had Peabo come in and sing the second verse. I think about this every time I hear it and try to imagine what it would sound like if it were completed. That's also why the second verse is a little scetchy and roberta flack was brought it to sing the "never comin down" with Peabo towards the end.
from:wikipedia
After Riperton died, several artists contributed vocals to tracks she had recorded before her death, to help compile Richard Rudolph's final tribute to his beloved wife, "Love Lives Forever." Included, among others, were Peabo Bryson, Michael Jackson, and Stevie Wonder.

Riperton's last single, "Give Me Time" was released in 1980. Richard Rudolph wrote the song, "Now That I Have You" for Riperton, but she never got the chance to record it; he gave the song to Teena Marie, who recorded it (and co-produced it with Rudolph) on Teena Marie's second LP, Lady T. Finally, in 1982, Capitol Records released The Best Of Minnie Riperton, a greatest hits collection.