If you mean S****, her whole life is about fighting. She died in a good fight. As for D****, he is considered Patient Zero. While trying to release the freaks, he got bit. When he returns to Capital City, he'll spread the infection to the main island and the rest of the world.
Based on lore, he will die spreading the infection at Capital City. So you're not going to play as him. If you played Dream City Apocalypse until the end, you'll discover the game takes place 200 years in the future acknowledging the apocalypse had already happened in the past. This was the apocalypse triggered by D****.