She has a lifetime contract, so maybe it isn’t the writers, but more of that. I imagine when she passes away in real life she will pass away on the show shortly after that. With her contract she is probably getting paid still and therefore killing her off on the show would not be right.
As for Mickey, I think right now is not the right time for Maggie to lose Mickey. She is turning into the new Mickey and once that transformation is done, I then see them doing that.