So we all know that everyone died from the beams of light but Kirby right? We watched characters attempt to escape the beams but ultimately failed. (I had to watch as 2 of my mains, Lucario and Greninja, die right next to each other. It hurt to watch.) But we didn't see everyone get hit. Of course, this is probably to save time for the rest of the trailer. But what if it wasn't? What if some characters escaped the light?
So by this logic we can assume that many characters did live, including most of the Fire Emblem characters, King Dedede, Pirhana Plant, Incineroar, etc.
(Lol this is my sad attempt at believing that King Dedede and Ike are still alive)