I think killing a boss enables a raid type; it doesn't necessarily disable them. I've killed the first four bosses, and I still get wolf, skeleton, blob, troll, fuling... maybe surtling? I think I've only seen drake once, and I haven't seen a greydwarf raid since early in my playthrough. I don't think I've seen draugr in awhile, although I still get the plain blob/ooze raids (both start with "a foul smell").

Raids are never going to stop, so I wouldn't worry about it. They're just a fact of life.