SOme mold spores can remain dormant for probably 1000's of years, and probably beyond your lifetime under some rather nasty conditions. Mold needs three things: food, moisture, and their existance to create problems. Take away any one, and it goes dormant. The least intrusive thing that kills them is probably a water/bleach solution. I'd try to rid myself of as many as possible. You'll never get rid of all of it, and new ones will be airborne to repopulate the area, but without all three legs of the triangle, it won't grow. Disoldging the spores can be a health problem; it's just when it's growing, it is producing lots, no new ones while it is dormant.