I agree. William J. Bell had been writing the show for a year by then, and DAYS was really rockin'; mesmerizing to watch. I imagine that the show's lack-luster first year had been disinteresting to soap fans who had tried it, so it took the audience a while to give Salem a second chance.
I remembered now - she had suggested they kill Mary off when she left. I guess they decided not to as they had successfully recast some other key roles, but they should have taken her up on it.
It was very classy of her to maintain such a good opinion of the show that she returned so many times (I think she also returned for some scenes in 1982 or 1983).
I know it shouldn't have been funny, but the show returning to flashbacks of her very, very soon after Mary was killed - even though she had left the role 2 years earlier - said it all.
Mulgrew did return years later, as a "ghost" during the years Yasmine Bleeth played her daughter. KM agreed to participate in the show's finale as well. The idea of reprising the role temporarily must not have been distasteful to her. I guess we'll never know for sure if TPTB approached her about coming back for Mary's death storyline, but it would have been so much more meaningful and effective if an actress we knew and loved in the role had been playing her in that end. With NG, I felt no loss when Mary Ryan passed. (And I might have cheered if the character had died while KT was there, LOL!)