With all this multiversal stuff. Theres no need to recast. Chadwick's t'challa can continue to be canon while are alternate one can be pulled from a different timeline or something. The people complaining about not recasting just lack creativity. Thats why Patrick Stewarts Professor Xavier and Tobey's Spiderman technically exists as part of the MCU now. Disney not recasting shyt anymore. Chadwicks black panther will always be Chadwicks black panther.
They might bring in a new T'challa at some point, same way Tom Holland is a new spiderman. But they not erasing Chadwick like ya'll want them to, because there is no reason to.