First off RIP to Chadwick. Such a devastating loss not only to us fans, but to his family as well.
Nobody should be cast as T’Challa. Marvel does well by their characters and even more so by their actors. There’s a reason all of these actors love being in the movies. The Marvel team has the utmost respect for them. It would be mad disrespectful to just throw somebody else in that role. They need to honor him in Black Panther 2.
That being said, I know it’s a long shot, but I think Marvel could pull this off.
Imagine at the end of Black Panther they didn’t let Killmonger die. They took him down and saved him. He’s in a coma but in the astral plane. Shit is fucked up in Wakanda and around the world with the sudden death of King T’Challa, especially his hometown in Compton because that became the Wakandan embassy in the US and was attacked and taken over.
He learns Wakandan history and pride from the ancestors and his place in that lineage being the rightful heir to the throne as the oldest living descendent in the bloodline. He has a change of heart but is struggling with his past actions. Never questions his motivations in the past, just his actions cause he still believes in helping the black race.
Comes out of the coma and has to don the Black Panther mantle to save Wakanda and his old hood. But he wears the Jaguar suit still because he doesn’t feel worthy of the Black Panther suit or name. Even goes by the Jaguar and denounces the Kilmonger name.
By the end of the movie he wins and earns the respect of everyone involved and is fully redeemed, yet he still struggles with his past actions and his worthiness. We expect him to be some the King and Black Panther, those in Wakanda push for it even, but he rejects it and Siri becomes queen with him acting as the protector under the Jaguar name.
At least until part 3 when Suri has to step down for whatever reason and he becomes the fully realized Black Panther and King. All the while we realize that the Black Panther trilogy was not really the story of T’Challa, but the story of Killmonger.
The only reason I wouldn’t go the Suri becomes Black Panther route is because she can’t carry a series of movies as the lead. But Michael B. Jordan can and he’s already a fan favorite.