If Chadwick's family would have wanted the opposite (BP not being recast) would you still want him recast?
I think the importance of the most prominent, and first, black superhero along with his brother saying that Chadwick understood the character was bigger than him (we can't get his opinion on the matter, but all indications seem to be he would have supported it), and the loss of the character in future Marvel stories are the most important factors - so yes. That they support it just further solidifies it.
I say this with respect and grace to the family -they don't own T'Challa. With equal respect and grace to the cast and director who suffered the loss of a friend, and colleague, they don't own T'Challa either. I could argue that not recasting him goes more against what he would have wanted.