2D Kirby isn't dead or anything, this isn't the last one we'll ever be getting. Kumazaki (series director now) says that they're not just abandoning it only because Forgotten Land did well. They plan to make more 2D Kirby games in the future with this kind of engine going forward, they'll likely swap back and forth between 2D and 3D depending on the story they want to tell. So this is far from the end, Deluxe just shows that 2D Kirby is still alive and kicking and will continue to do so. Unless we get a Kirby Maker in the vein of Super Mario Maker, it's here to stay.