My own parents gave up shunning me after I was disfellowshipped. They kept it up for about 3 years and then just sort of gradually folded.
Here in WSM, most of the witnesses who remember me can't be arsed with the shunning thang any more. Even the devout witness lady who works in Marks & Sparks enjoys the occasional little giggle with me across the deli counter.
When my best pal was DF'd, my shunning of him lasted just over a year before I started to speak to him once more in defiance of the WT ban. The relief that I felt was indescribable when we first resumed talking. It gave me a real warm glow inside.
See, I think that shunning someone is a really un-natural thing to impose on someone. It goes against all of our instincts if that person hasn't personally hurt us. I just don't think it's possible for a normal person to keep it up for ever if it involves a relative or close friend. I'd be surprised if many can keep it up for more than a few years.
Englishman.