The MIA's are still there, or I should say everywhere. With a little bit of luck they will settle to the bottom of the block. They are not likely to do any damage but if it really bothers you, remove the thermostat and backflush, backflush, backflush until you feel comfortable that you got enough of it out. Backflush with a hose in the coolant bottle and the thermostat houshing open to the air so that you float everything you can from the blosck and the radiator. Other than that the only answer is to start tearing things down until you feel that you have cleaned it to your satisfaction. I don't think you really need to do all of this.
