At this point HM...I would suggest to do whatever itis YOU want to do. If writing a letter would make you feel a sense of closure then do it...you have nothing to lose and in the end if that is the only thing you have gained...that is better than before.
I would be careful to enter it with no expectations...
I did write a letter to my former mother in law who was very in touch with the fact that her son is a sociopath (diagnosed by the way...and she fully knew)
I remained in contact with them for a bit but the situation became too awkward for me and confusing for my children since he was their step-dad, albeit the only dad they had really known...
it was painful and awkward and I dreaded running into him and...in the end...they were not my family...there were too many lies and things overlooked or looked past. I have random contact with his sister and brother and their respective spouses but more in passing and nothing deep.
if you would not feel rejected if they did not reach out to you then I say go for it...if you would then I would reconsider
