It can be cathartic to write such letters but honestly, they probably won't do much. You said in your letter you choose not to have contact unless it's about the children. No need to tell her that, just start doing it. She may notice, she may not but either way it will give you some space so YOU can decide what YOU need for YOU.
*IF* the WAS ever snaps out of it (and that is a big, fat if) it has to be on their timeline and rarely does that timeline match up with the one the LBS has in mind.
I am unsure what you mean by an "end game"? Does that mean a divorce or something else?
