Hi Jules, when my husband and I left we believed the JWs had been the true religion but had become corrupt like ancient Israel. So at the time we thought the right thing to do was disassociate and try and find the 'truth'. Sometimes I've regretted it because I lost all my family and we lost all our friends.
However it was a clean break for us, we started a new life. We both studied for distance learning degrees, got proper jobs, bought a little house, had a child. There's a lot to be said for starting again. It cleared our minds and allowed us to read whatever we wanted and do whatever we liked. Nobody was breathing down our necks, judging everything we did because they didn't know. Nor were they trying to get us to return and confusing us with love bombing.
My family have shown themselves to be very mentally unhealthy because even though we made it quite plain we're never going back and we no longer believe in any religion or try and preach at them they still insist on treating me and my daughter as lepers. It's been twenty-eight years. So whatever my early religious life had been I would have had to find some distance from them eventually because they are so screwed up.
Your grandfather, on the other hand, sounds like a very mentally healthy person, leaving because the religion tried to make him put strangers before family. He's a really together person who recognises cult speak when he hears it. I'm glad you have him as support if all else fails with your parents.
I'm not telling you to disassociate by the way, just answering your question with my personal experience as you asked.