I disassociated a while back. It was what I had to do to move on. I was not going to fade and still have murmuring about me. Nagging family about what I was doing. I could not bear to spend the rest of my life looking over my shoulder wondering if every time I was doing something "unscriptural" if someone would see me. More importantly if you fade you are still a JW. The thought of that repulsed me.
Writing a letter to leave an organization is not unique to jw land. Resignation letters etc...
what at this comes down to is what you can handle. If you can bear to face the possibility of never speaking to your family again with the upside of being your true self then write a letter.
Otherwise you you can fade. Both have their own personal advantages and disadvantages just be very careful and really think your decision through