It's not like Donna Reed at all though. Reed's Miss Ellie was a big change in character. And correct me if I'm wrong, but didn't Swansong (the Dallas episode with Bobby's death) do better in the ratings than Royal Wedding (the Dynasty episode with the Moldavian Massacre)? Those two episodes both went out on the same week in the USA, Royal Wedding on Wednesday 15 May 1985 and Swansong on Friday 17 May 1985.
The Mis-Ellie recasting in fact hurt DALLAS during Season 8 (per DVD) not the writing so much; even at the time, the recasting felt so bizarre and tone deaf that it cast a tonal pall over the year.
The death of Bobby outrated the Moldavian massacre because DALLAS -- and its cliffhangers -- were character-based while DYNASTY was not. So that gave the impact of a single character on DALLAS much greater impact.
I like Margaret Michaels, but recasting core characters in nighttime shows is just too risky, and the success rate for it isn't good. I mean, it was apparently discussed after Jim Davis died as to whether or not they should recast Jock --- and they mercifully voted against it... Sure, Jim Davis had died, but even if he'd left the show over health reasons, a "new" Jock would have been the same disaster that re-casting Miss Ellie.
Why would Pam be any different?