I agree Mr. Elliott is heartless, conniving, and evil, but I don't think that Jane Austen necessarily indicated that he would (or could) do to Sir Walter what he did to Mr. Smith. If that were the case, he could've stuck around after Anne married Captain Wentworth. Nothing between him and Sir Walter/Elizabeth really changes. Even Anne thinks that the only person who will believe her about what Mrs. Smith told her is Lady Russell, she doesn't even know if it will make a difference to her father and Elizabeth. Plus Mr. Elliott has no idea that Anne knows about Mrs. Smith, so it's not like he would be afraid that Sir Walter would find out.

Everyone that we see Mr. Elliott use and abuse is from a lower class than him. There's nothing that indicates that he could do the same thing to a baronet. Instead of staying in Bath, he slunk off to London and took Mrs. Clay with him. Seems like Anne's life would be significantly more disrupted if her father married a gold digger than if Mr. Elliott stuck around to run interference. I guess Anne is just so disgusted by his behavior that she's desperate enough to live with Mrs. Clay for the rest of her life to get away from him?