I know what you mean about wanting a clean sweep - closure - I too wanted that so I did send them a letter listing my desire to separate myself from the WTS and my reasons for so doing. It felt good to take that action - and like I was honoring Jehovah in so doing. It is an excellent opportunity to "witness" to those who have been misled - at least the elders who will read your letter and who knows what effect it may have that will be beneficial for them. Every letter they get of this nature has to have some effect - be sure of that. It will rankle in their minds - maybe for many years but some may eventually investigate.
To give you an example - many years before an older brother of the anointed suggested I should read Ray Franz book. He was still inside the organization at that time and may still be - I do not know. I was shocked and wouldn't consider it and considered he was in terrible danger doing what he had done. But the day came years later I did finally read one of the books Ray Franz had written and that was all it took. So I made it a point to give the brothers a list of the books they might read to understand my position knowing some day they could possibly look one of them up. Turns out the PO that came to visit me for the "exit" interview confessed he had started to read Ray Franz first book - Crisis of Conscience many years before but not finished it. That night they were here I explained the material about the Malawi Party Card to them and they didn't believe I could be right. Someday I am sure they will check it out and will be surprised.
Of course it is not fun to have old friends shun you when you meet them out in public but I have survived and only feel saddened now that they feel constrained so by the organization to carry out that behavior. One dear friend did recently come to visit me after a whole year had gone by and apologized for taking part in that action. That was a great experience.
In your case - your having been gone so long I do not know what they will endeavor to do. It is possible they may send some local yokel to make a personal call on you and make one final effort to twist your arm. But you can survive that and possibly be an aid to helping those poor souls who do call on you. Just consider them your "Bible Studies" for the moment but try to avert arguments. They never achieve anything good for either side. Make your case concise and simple and then step back and let them know case closed if it appears they are not sincere in trying to understand. In my case they unloaded a lot of their troubles to me that night - admitted things were actually much worse than I even knew about - so it may be Jehovah will use you on that occasion. Just keep your channel of prayer to Him going all the time they are there - it helps greatly.
Also recently one of those elders called at my door in his regular field service ministry - I think unintentionally by the look of total shock and surprise in his face when I answered the door - but we were able to visit personably - his partner didn't feel comfortable - but he did and we parted company with a wishing each other well - another amazing experience. As time goes on I notice some now smile and nod at me in the grocery store instead of "the cold stony look straight ahead and pretend they never saw you" stupidity so that too is an improvement. Wouldn't it be nice if the day came they actually saw fit to stop the shunning business - dream on - I know it is not going to happen - but that doesn't keep me from hope.
What you do needs to be a matter of prayer between you and God. There are pro's and con's either way.