I don't think there really is a REAL closure regardless of how long you have been gone.
For those of us who were never really 'in' but have family 'in', we'll never have complete closure until they die or get out.
I have many questions which are slowly being answered that have validated what I felt and concluded about this organization when I was a teen in the 1970s. A heavy toll has been paid in my family because of the WTS and that burden will always be there. You cannot go back and change the past. The damage created still exists today.
Your analogy of a divorce is a good one. Divorce has been compared to a type of death. However you look at it, when you decide to leave, an end has occurred. Now the 'change cycle' begins ( http://www.changecycle.com/changecycle.htm ). Sometimes it takes people years to move through the different stages, especially if the change is of the magnitude most heavily indoctrinated JWs experience. Some people never make it out of the first 3 stages. I believe this is why some go back. To find closure, you need to move through the remaining stages of the change cycle, and ultimately, for JWs, redefine your life. It is an enormously challenging task for some. Hence, my statements in the past about mentors needed for those who truly wish to move forward, away from their previous life as a JW. Reprogramming the mind is all part of this process. Closure comes when your present life fulfills you to the point where the painful past is no longer hurtful or important to you. Sometimes that comes quickly, other times, much more slowly, and in a few cases, not at all. It's a choice and it differs for all of us.