Donald Draper wrote:
If they do not kill the character her role will have to be changed. I can not see the current status of Moria trying to undermine, kill Malcolm, why hiding it from her kids lasting too long.
Let her succeed, kill Tommy's father, let Oliver find out some things but not all of it. They can keep her around, it's not that hard, the audience accepts a lot in comic book shows, look how long they managed to keep Lionel Luthor on Smallville.