It sounds like they were pretty sick.  Still, after they recover they should go back to laying well.  DE is pretty useless in treating worms or anything else.  Valbazen and SafeGuard Liquid Goat Wormer are 2 very good wormers.  Dosage is 1/2 ml by mouth for average size birds, and repeat in 10 days.  Many worm twice a year, more or less, depending on how warm and wet your environment is.  Certain chicken worms (capillaria, tapeworm, or gapeworm) may need higher dosages and for several days, but a vet could perform a fecal float if you suspect a problem.  Chickens can take breaks from laying for all kinds of reasons including heat of summer, cold in winter, molting season, and from diseases and worms.