There would always be a portion that would shun whether it's official policy or not. Especially those who have spent their entire lives with that mindset. Over time, there would be a general relaxing which would lead more people to feel free to walk away. I'm PIMO and would walk away if I thought my family wouldn't shun me. Honestly, I'm pretty sure that most of them would not. My MIL definitely would which would bother my wife.
Immediately, I'm not sure it would even be 10% because the practice of shunning is so ingrained.