What if they'd said yes?

A game for opera nuts:

The following list is of famous singers and roles they never sang but were offered. Which ones make you glad they said No? Which ones are dreamy might-have-beens?

Joan Sutherland - Louise
Kirstin Flagstad - Marschallin
Tatiana Troyanos - Cassandra
Leontyne Price - Desdemona
Renata Tebaldi - Norma
Victoria de los Angeles - Adalgisa
Leontyne Price - Abigaille
Maria Callas - Vanessa
Kirstin Flagstad - Norma
Tatiana Troyanos - Idamante
Joan Sutherland - Konstanze
Leontyne Price - Vanessa
Birgit Nilsson - Carmen
Lotte Lehmann - Kaiserin

Any others? (I'm sure there are thousands - Nicolai Gedda said 80 percent of a career is saying No, and he sang everything.)