You don't want to delete the ancestor if they have spouses or multiple children (ie aunts and uncles to you). You want to get rid of the aunts and uncles (to you) and spouses first.
That said, you haven't explained if you have entered persons peripheral to this ancestor. Prior and subsequent spouses of ancestors in that line, children of prior and subsequent spouses from subsequent or prior marriages, etc.
Does this non-ancestor mean that it invalidates a whole ancestral line? Or, just invalidates that this person is parent of someone who is an ancestor?