I believe top Marvel brass knew - probably one of the reasons BP’s role was not as prominent as it could have been over IW and EG. The big question is whether they’ll attempt to re-cast, or launch directly into Shuri as BP.
With the de-aging / facial tech they’ve already used for various people in the Infinity Saga, I can see them briefly using a stand in actor w/ Chadwick’s face in order to at least explain away his disappearance. I don’t know if I like that though.
Had a wild thought of them inviting back Michael B. Jordan to continue as T’Challa. I think the fandom generally would be understanding and supportive.
From an emotional perspective right now, I hope they let the character rest - Chadwick made T’Challa who he is. Perfect casting.
Who knows? Feige and Coogler probably do though.