I think that if you have never been estranged it is quite difficult to get your head round, as a concept.
A friend of mine has not had contact with her mother for many years, although they used to live in the same village, so would sometimes bump into each other but not speak. I remember being absolutely shocked at this, as I was close to my own DP and couldn't imagine a situation where a human being has given birth to another human being but could pass each other in the street without speaking. My friend explained the reasons and of course I did not tell her that she should contact her DM, as it was clearly a hard decision which she had reached, but I felt so sorry for her, so desperately sad, as I loved my own DC so much. I accepted what she said but I didn't understand, not really.
Fast forward a number of years and, having gone through a very painful period of estrangement from DD1, to whom I was close (she said I was her best friend and role model), I can see how these situations can arise. Even the strongest relationships can be fragile.
I am sure that your friend means well, but it isn't her business. It is up to your DH. However, I wonder, since you have posted, whether you feel that your DH has made the right decision.