Well, in this case, those in charge of the MCU were able to swap out Edward Norton for Mark Ruffalo with little fuss, so I imagine they'll find another actor to take Mr. Boseman's place That successor will have some huge claws to fill, but I, for one, would want to see the character go on, especially in a direct sequel. There were a huge number of really good actors in Black Panther, and it would be a shame to not see them in their MCU roles again on account of Marvel losing their lead actor.
Rest You Well, Mr. Boseman--and Thank You for lending your talent to one of the best Marvel movies ever made.