I think part of it might be the attitude of the shunner. There's always partial responsibility, but, degrees vary depending on their approach.
For example, if my younger sister ever had to shun me, it would absolutely break her heart. She would be tormented by it and for me, there would be nothing to forgive if she ever figured out ttatt.
My younger brother, on the other hand, actively shuns me even though I've just faded. So much so that I can't even meet his newborn. Not as easy to forgive...