Certain ones disappear, but the raids related to the next boss will start. Additionally, other types of raids will start happening once the right conditions are met (i.e. killing a certain boss and/or killing some other creature), and they won't ever go away. One example of this is the blobs that start raiding from the swamp after Bonemass is killed. I don't like raids because I want to build in peace and don't like fighting in general, so I build in a world in which no bosses get killed. This guarantees that I only get raided by necks and boars.