There is no easy answer. I struggled with it for years. In the 18 years since I left, there have been many Witnesses who have died, where I wanted to go to the funeral. I only went to one, 8 years ago, and two funeral home visitations for others.
At the first visitation, I had just left the Witnesses and was really f@#!ed up. A Sister came up to me and asked me something and I said, "I don't want to talk about it." Then I left. I wasn't ready for this kind of public appearance.
Ten years later I went to a funeral at a Kingdom Hall (because the deceased had been exceptionally nice to me) and I was ready. Nobody really talked to me which was fine. I wasn't dissassociated yet. You could tell some were surprised to see me. Others didn't even recognize me. I listened to the talk...well, sort of. I felt like I was visiting Mars.
Finally I got the fear of attending a Witness function out of my system. I always wondered if I'd sit there and go "I've go to run back." The opposite in fact happened. I had a kind of peace about it.
I still won't go to Witness funerals as a rule only because I've been very public about my life and the notoriety of my presence might be upstage the real reason I went: to show sympathy. It ain't worth it in my case. I send cards/flowers.
Finally the fact that I'd have to plan my Witness mother's funeral plagued me for years until I did something about it. [all four of her kids are either disf or disas.] I discussed it with my mother and she agreed to all my plans. I prepaid for a funeral at a funeral home. There will be no Elder giving a talk. [Imagine an Elder comforting us who could not talk to us!! Ridiculous] No newspaper announcement until after the funeral takes place. I don't want no surprises. People will be informed, invited to attend the service. People can go up and remember her. In respect for her faith, I will ask her Witness female friend, if she'd like to read a few scriptures. [She can wear a head covering if she'd feel better]. This way the children of my mother, their feelings are of paramount consideration. My mother feels better about this plan too.