Letter or no letter....NC or Dark...
Where the MLCer is, and where the LBS is determines the answer.
I believe uber monster requires a letter and NC. It states your boundary in black and white, so they can reread it when their swiss cheese memory fails. Especially if you are doing a 180 and stopping pursuaing behaviors. It is a clear, calm expression of your boundary that you will not be in contact with them at all, for any reason. Without the letter, some MLCers see it as a controlling tactic to manipulate them. Some will see it that way anyway, but after many readings, it may sinl in. It must be simple, direct, no examples, complaints, or emotions. To go "no contact", the lbs has to be in strong place, and must maintain NC until monster subsides. It is a boundary YOU must not cross. It is for you! Eventually, it may be possible to move into Dark, and move in and out at your discretion.
NC is not a strategy to change your mlcers behavior. It is a protective bubble you put around yourself, so that you can get out of the drama and get your feet under you. Technically it involves indirect contact as well. That means, you are working on getting them out of your head and focusing on your own day to day stuff. It means you do not listen to tales of their antics from friends and family, you do not ask people about them, you do not give them any head space. It also means blocking their emails, texts and calls. The only contact that gets through to you involves financial and kid arrangements through an intermediary. this person must be instructed to filter out all other messages not directly related to business and kids. You do not need to hear "That bit*& is nuts," or "I miss talking to her".
A letter most likely will amp up monster for awhile. If the LBS doesn't cave, it will stop, and peace will come. If the LBS caves and turns it into an opportunity for more R talk, the MLCer will see it as a manipulation tactic, the LBS will feel worse and be in the same position as before.
Most of us have "gone dark" at some point, if we are not pursuing. This all by itself, does not require any formal statement. It is more simple behavioral training. Many, like mitzpah, have had our MLCers go dark on us. These are opportunities to focus on you, get out of the drama, stop the spinning, and create peace around you.
RCR has an excellent article on NC here:
http://www.midlifecrisismarriageadvocate.com/standing-actions_contact-and-communication_contact-levels_no-contact.htmlThe whole series is excellent.
AND I agree with OP, post your communcations for review, and WAIT 48 hours before responding to avoid reacting.