Sometimes the fight between two family members lasts for the rest of their lives. It can impact how much children or grandchildren know about certain family members. It can impact how family ephemera gets passed down from one generation to another. It can impact how individuals do not know they have first cousins living fifteen miles away.
It can be difficult to say how an estrangement can impact those left behind, but the genealogical impact can last for generations.
Family may need to be found to settle up an estate but their only communication could be through their lawyers.